django: a página é atualizada quando clico em importar arquivo e nenhuma mensagem aparece

Estou trabalhando em um aplicativo web com Django e quero personalizar a visualização do administrador de um dos meus modelos. Criei um modelo personalizado para adicionar a página e substituí a função salvar na classe de administração para processar o arquivo de entrada antes de salvar.

aqui tenho a classe admin do RMABGD:

@admin.register(RMABGD)
class RMABGDAdmin(BaseModelAdmin):
    list_display = ('name', 'code_RMA', 'type_BGD', 'Partenaire', 'date_creation', 'RMA_BGD_state')
    list_filter = ('type_BGD', 'RMA_BGD_state', 'city')
    search_fields = ('name', 'code_RMA', 'Partenaire')

    add_form_template = "admin/spatial_data/RMABGD/change_form.html"
    change_form_template = "admin/spatial_data/RMABGD/change_form.html"

    def process_excel_import(self, request):
        excel_file = request.FILES.get('excel_file')
        if not excel_file:
            messages.error(request, "No file was selected. Please choose an Excel file.")
            return False
        try:
            df = pd.read_excel(excel_file)

            required_headers = ["code RMA", "code ACAPS", "Dénomination RMA", "Ville", "Adresse", "Longitude", "Latitude", "Type BGD", "Partenaire", "Date création", "Etat BGD RMA"]
            missing_headers = [header for header in required_headers if header not in df.columns]

            if missing_headers:
                messages.error(request, f"Missing required fields: {', '.join(missing_headers)}")
                return False
            else:
                # If all headers are correct, process data
                rows_imported = 0
                errors = 0
                for index, row in df.iterrows():
                    try:
                        # Process row data
                        obj = RMABGD(
                            code_ACAPS=row["code ACAPS"],
                            code_RMA=row["code RMA"],
                            name=row["Dénomination RMA"],
                            address=row["Adresse"],
                            city=row["Ville"],
                            location=f'POINT({row["Longitude"]} {row["Latitude"]})',
                            type_BGD=row["Type BGD"],
                            Partenaire=row["Partenaire"],
                            date_creation=row["Date création"],
                            RMA_BGD_state=row["Etat BGD RMA"]
                        )
                        obj.save()
                        rows_imported += 1
                    except Exception as e:
                        messages.error(request, f"Error in row {index + 1}: {str(e)}")
                        errors += 1

                if rows_imported > 0:
                    messages.success(request, f"Successfully imported {rows_imported} rows")
                    return True
                if errors > 0:
                    messages.warning(request, f"Failed to import {errors} rows. See details above.")
                if rows_imported == 0:
                    messages.error(request, "No rows were imported. Please check your file and try again.")
                return rows_imported > 0
        except Exception as e:
            messages.error(request, f"Error processing file: {str(e)}")
            return False
    
    def save_model(self, request, obj, form, change):
        self.process_excel_import(request)
        super().save_model(request, obj, form, change)

e este é o modelo correspondente para adicionar:

{% extends "admin/base_site.html" %}
{% load i18n admin_urls static %}

{% block content %}
<div id="content-main">
    {% if messages %}
    <ul class="messagelist">
        {% for message in messages %}
        <li{% if message.tags %} class="{{ message.tags }}"{% endif %}>{{ message }}</li>
        {% endfor %}
    </ul>
    {% endif %}

    <form action="." method="post" enctype="multipart/form-data">
        {% csrf_token %}
        <div>
            <fieldset class="module aligned">
                <div class="form-row">
                    <div class="fieldBox">
                        <label for="id_excel_file" class="required">Excel File:</label>
                        <input type="file" name="excel_file" id="id_excel_file" accept=".xlsx,.xls" required>
                        <div class="help">Upload an Excel file with the required columns</div>
                    </div>
                </div>
            </fieldset>

            <div class="help-text">
                <p><strong>{% trans 'Required fields in the imported file:' %}</strong></p>
                <ul>
                    <li>code RMA</li>
                    <li>code ACAPS</li>
                    <li>Dénomination RMA</li>
                    <li>Ville</li>
                    <li>Adresse</li>
                    <li>Longitude</li>
                    <li>Latitude</li>
                    <li>Type BGD</li>
                    <li>Partenaire</li>
                    <li>Date création</li>
                    <li>Etat BGD RMA</li>
                </ul>
            </div>

            <div class="submit-row">
                <input type="submit" value="{% trans 'Import Excel' %}" class="default" name="_import_file">
            </div>
        </div>
    </form>
</div>
{% endblock %}

quando clico em importar arquivo, a página é atualizada e nenhuma mensagem é exibida como se a função de arquivo de processo não tivesse sido executada