Fix bug of branches API with tests(#25578) (#25579)

Backport #25578 

This PR added a repository's check when creating/deleting branches via
API. Mirror repository and archive repository cannot do that.

models/fixtures/mirror.yml

@@ -0,0 +1,49 @@
+-
+  id: 1
+  repo_id: 5
+  interval: 3600
+  enable_prune: false
+  updated_unix: 0
+  next_update_unix: 0
+  lfs_enabled: false
+  lfs_endpoint: ""
+
+-
+  id: 2
+  repo_id: 25
+  interval: 3600
+  enable_prune: false
+  updated_unix: 0
+  next_update_unix: 0
+  lfs_enabled: false
+  lfs_endpoint: ""
+
+-
+  id: 3
+  repo_id: 26
+  interval: 3600
+  enable_prune: false
+  updated_unix: 0
+  next_update_unix: 0
+  lfs_enabled: false
+  lfs_endpoint: ""
+
+-
+  id: 4
+  repo_id: 27
+  interval: 3600
+  enable_prune: false
+  updated_unix: 0
+  next_update_unix: 0
+  lfs_enabled: false
+  lfs_endpoint: ""
+
+-
+  id: 5
+  repo_id: 28
+  interval: 3600
+  enable_prune: false
+  updated_unix: 0
+  next_update_unix: 0
+  lfs_enabled: false
+  lfs_endpoint: ""

models/fixtures/repository.yml

@@ -141,7 +141,7 @@
   num_projects: 0
   num_closed_projects: 0
   is_private: true
-  is_empty: true
+  is_empty: false
   is_archived: false
   is_mirror: true
   status: 0