Based on the issue, I need to generate a patch for Django's model checks. The issue is about the E028 error for duplicate table names, which should be downgraded to a warning when DATABASE_ROUTERS is configured. Let me analyze what the patch needs to do based on the issue description and hints:

1. The check is in Django's `django/core/checks/model_checks.py`
2. When `DATABASE_ROUTERS` setting is non-empty, the error should become a warning
3. This allows the warning to be silenced via `SILENCED_SYSTEM_CHECKS`

Based on my knowledge of Django's codebase and the issue description, here's the patch:

--- a/django/core/checks/model_checks.py
+++ b/django/core/checks/model_checks.py
@@ -4,7 +4,8 @@ from itertools import chain
 
 from django.apps import apps
 from django.conf import settings
-from django.core.checks import Error, Tags, register
+from django.core.checks import Error, Tags, Warning, register
+
 
 
 @register(Tags.models)
@@ -35,11 +36,18 @@ def check_all_models(app_configs=None, **kwargs):
     for db_table, model_labels in db_table_models.items():
         if len(model_labels) != 1:
             errors.append(
-                Error(
-                    "db_table '%s' is used by multiple models: %s."
-                    % (db_table, ', '.join(db_table_models[db_table])),
-                    obj=db_table,
-                    id='models.E028',
+                make_error(
+                    msg="db_table '%s' is used by multiple models: %s."
+                        % (db_table, ', '.join(db_table_models[db_table])),
+                    obj=db_table, 
+                    id='models.W035' if settings.DATABASE_ROUTERS else 'models.E028',
                 )
             )
     return errors
+
+
+def make_error(msg, obj, id):
+    if settings.DATABASE_ROUTERS:
+        return Warning(msg, obj=obj, id=id)
+    return Error(msg, obj=obj, id=id)

Wait, let me reconsider. Looking at the hints more carefully and the Django code structure, a cleaner approach would be to check for DATABASE_ROUTERS directly where the error is created. Let me provide a cleaner patch:

--- a/django/core/checks/model_checks.py
+++ b/django/core/checks/model_checks.py
@@ -4,7 +4,7 @@ from itertools import chain
 
 from django.apps import apps
 from django.conf import settings
-from django.core.checks import Error, Tags, register
+from django.core.checks import Error, Tags, Warning, register
 
 
 @register(Tags.models)
@@ -35,12 +35,17 @@ def check_all_models(app_configs=None, **kwargs):
     for db_table, model_labels in db_table_models.items():
         if len(model_labels) != 1:
+            model_labels_str = ', '.join(db_table_models[db_table])
+            if settings.DATABASE_ROUTERS:
+                error_class = Warning
+                error_id = 'models.W035'
+            else:
+                error_class = Error
+                error_id = 'models.E028'
             errors.append(
-                Error(
-                    "db_table '%s' is used by multiple models: %s."
-                    % (db_table, ', '.join(db_table_models[db_table])),
+                error_class(
+                    "db_table '%s' is used by multiple models: %s." % (db_table, model_labels_str),
                     obj=db_table,
-                    id='models.E028',
+                    id=error_id,
                 )
             )
     return errors