title: Django admin getting 400 while trying to upload multiple files from admin panel
body: <p>I am trying to upload images from .zip archive and data that relates for them from .xlsx.</p>
  
  <p>Here is admin.py file where I am trying to import images</p>
  
  <pre><code>@admin.register(ImageModel)
  
  class ImageAdmin(admin.ModelAdmin):
      change_list_template = "entities/images_changelist.html"
      list_display = ('name', 'img')
      @staticmethod
      def img(obj):
          return mark_safe(
              f'&lt;img src="{obj.image.url}" height="100"&gt;') if obj.image else None
  
  def get_urls(self):
      urls = super().get_urls()
      my_urls = [
          path('import-images/', self.import_images),
      ]
      return my_urls + urls
  
  def import_images(self, request):
      form = forms.ImagesUploadForm()
      if request.method == "POST":
  
           ...Parsing them...
           self.message_user(request, "Your images have been imported")
           return redirect('/admin/images/imagemodel/')
  
      return render(request, "admin/images_form.html", {"form": form})
  </code></pre>
  
  <p>Here is html of form:
  {% extends 'admin/base.html' %}</p>
  
  <pre><code>{% block content %}
      &lt;div&gt;
          &lt;form action="." method="POST" enctype="multipart/form-data"&gt;
              {% csrf_token %}
              {{ form.as_p }}
              &lt;button type="submit"&gt;Import images&lt;/button&gt;
  
          &lt;/form&gt;
      &lt;/div&gt; 
      {% endblock %}
  </code></pre>
  
  <p>Here is my form:</p>
  
  <pre><code>class ImagesUploadForm(forms.Form):
      excel_file = forms.FileField()
      zip_file = forms.FileField()
  </code></pre>
  
  <p>It works good on my local machine but I am getting 400 error on my dev server. Also when I'm adding <code>if form.is_valid():</code> I always get <code>False</code> and <code>form.errors == ''</code></p>