Python: Use mimetype instead of content-type in django modeling

This enables the XSS query to actually find results from django responses.

python/ql/test/experimental/library-tests/frameworks/django-v1/response_test.py

@@ -18,19 +18,19 @@ def safe__manual_content_type(request):
 # XSS FP reported in https://github.com/github/codeql/issues/3466
 # Note: This should be an open-redirect sink, but not an XSS sink.
 def or__redirect(request):
-    return HttpResponseRedirect(request.GET.get("next"))  # $HttpResponse mimetype="text/html; charset=utf-8" responseBody=Attribute()
+    return HttpResponseRedirect(request.GET.get("next"))  # $HttpResponse mimetype=text/html responseBody=Attribute()
 
 # Ensure that simple subclasses are still vuln to XSS
 def xss__not_found(request):
-    return HttpResponseNotFound(request.GET.get("name"))  # $HttpResponse mimetype="text/html; charset=utf-8" responseBody=Attribute()
+    return HttpResponseNotFound(request.GET.get("name"))  # $HttpResponse mimetype=text/html responseBody=Attribute()
 
 # Ensure we still have an XSS sink when manually setting the content_type to HTML
 def xss__manual_response_type(request):
     return HttpResponse(request.GET.get("name"), content_type="text/html; charset=utf-8")  # $HttpResponse mimetype=text/html responseBody=Attribute()
 
 def xss__write(request):
-    response = HttpResponse()  # $HttpResponse mimetype="text/html; charset=utf-8"
-    response.write(request.GET.get("name"))  # $HttpResponse mimetype="text/html; charset=utf-8" responseBody=Attribute()
+    response = HttpResponse()  # $HttpResponse mimetype=text/html
+    response.write(request.GET.get("name"))  # $HttpResponse mimetype=text/html responseBody=Attribute()
 
 # This is safe but probably a bug if the argument to `write` is not a result of `json.dumps` or similar.
 def safe__write_json(request):
@@ -50,4 +50,4 @@ class CustomJsonResponse(JsonResponse):
         super().__init__(content, *args, content_type="text/html", **kwargs)
 
 def safe__custom_json_response(request):
-    return CustomJsonResponse("ACME Responses", {"foo": request.GET.get("foo")})  # $HttpResponse mimetype=application/json MISSING: responseBody=Dict SPURIOUS: responseBody="ACME Responses"
+    return CustomJsonResponse("ACME Responses", {"foo": request.GET.get("foo")})  # $HttpResponse mimetype=application/json MISSING: responseBody=Dict SPURIOUS: responseBody="ACME Responses"