[4.1.x] Fixed #33800 -- Fixed system check for the same template tag module in installed apps and template tag libraries.

Thanks Claude Paroz for the report.

Regression in 004b4620f6f4ad87261e149898940f2dcd5757ef.
Backport of 083bfca6b6c00d0f45837a65c2db721eaf46bc07 from main

2 files changed, 17 insertions, 4 deletions

diff --git a/django/core/checks/templates.py b/django/core/checks/templates.py
index 5214276987..692ec98203 100644
--- a/django/core/checks/templates.py
+++ b/django/core/checks/templates.py
@@ -50,15 +50,15 @@ def check_string_if_invalid_is_string(app_configs, **kwargs):
 @register(Tags.templates)
 def check_for_template_tags_with_the_same_name(app_configs, **kwargs):
     errors = []
-    libraries = defaultdict(list)
+    libraries = defaultdict(set)
 
     for conf in settings.TEMPLATES:
         custom_libraries = conf.get("OPTIONS", {}).get("libraries", {})
         for module_name, module_path in custom_libraries.items():
-            libraries[module_name].append(module_path)
+            libraries[module_name].add(module_path)
 
     for module_name, module_path in get_template_tag_modules():
-        libraries[module_name].append(module_path)
+        libraries[module_name].add(module_path)
 
     for library_name, items in libraries.items():
         if len(items) > 1:
@@ -66,7 +66,7 @@ def check_for_template_tags_with_the_same_name(app_configs, **kwargs):
                 Error(
                     E003.msg.format(
                         repr(library_name),
-                        ", ".join(repr(item) for item in items),
+                        ", ".join(repr(item) for item in sorted(items)),
                     ),
                     id=E003.id,
                 )
diff --git a/tests/check_framework/test_templates.py b/tests/check_framework/test_templates.py
index 352a017e55..439097f1e1 100644
--- a/tests/check_framework/test_templates.py
+++ b/tests/check_framework/test_templates.py
@@ -161,6 +161,19 @@ class CheckTemplateTagLibrariesWithSameName(SimpleTestCase):
     @override_settings(
         INSTALLED_APPS=["check_framework.template_test_apps.same_tags_app_1"]
     )
+    def test_template_tags_same_library_in_installed_apps_libraries(self):
+        with self.settings(
+            TEMPLATES=[
+                self.get_settings(
+                    "same_tags", "same_tags_app_1.templatetags.same_tags"
+                ),
+            ]
+        ):
+            self.assertEqual(check_for_template_tags_with_the_same_name(None), [])
+
+    @override_settings(
+        INSTALLED_APPS=["check_framework.template_test_apps.same_tags_app_1"]
+    )
     def test_template_tags_with_same_library_name_and_module_name(self):
         with self.settings(
             TEMPLATES=[