fix calReleaseNumCommitsBehind (#24148)

`repoCtx.CommitsCount` is not reliably the commit count of the default
branch (Repository.GetCommitsCount depends on what is currently
displayed).

For instance on the releases page the commit count is correct:
https://codeberg.org/Codeberg/pages-server/releases


![2023-04-15-215027](https://user-images.githubusercontent.com/3864879/232250500-6c05dc00-7030-4ec9-87f1-18c7797d36bf.png)

However it is not on the single page:
https://codeberg.org/Codeberg/pages-server/releases/tag/v4.6.2


![2023-04-15-215036](https://user-images.githubusercontent.com/3864879/232250503-620c8038-7c2c-45a1-b99d-cb994ef955a6.png)

This PR fixes this by removing a "fast branch" which was using this
field (I think this field should be removed, since it is a bit
unpredictable - but this would mean a larger refactoring PR).

_contributed in the context of @forgejo_

---------

Co-authored-by: Giteabot <teabot@gitea.io>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

models/fixtures/release.yml

@@ -66,3 +66,45 @@
   is_prerelease: true
   is_tag: false
   created_unix: 946684800
+
+- id: 6
+  repo_id: 57
+  publisher_id: 2
+  tag_name: "v1.0"
+  lower_tag_name: "v1.0"
+  target: "main"
+  title: "v1.0"
+  sha1: "a8a700e8c644c783ba2c6e742bb81bf91e244bff"
+  num_commits: 3
+  is_draft: false
+  is_prerelease: false
+  is_tag: false
+  created_unix: 946684801
+
+- id: 7
+  repo_id: 57
+  publisher_id: 2
+  tag_name: "v1.1"
+  lower_tag_name: "v1.1"
+  target: "main"
+  title: "v1.1"
+  sha1: "cef06e48f2642cd0dc9597b4bea09f4b3f74aad6"
+  num_commits: 5
+  is_draft: false
+  is_prerelease: false
+  is_tag: false
+  created_unix: 946684802
+
+- id: 8
+  repo_id: 57
+  publisher_id: 2
+  tag_name: "v2.0"
+  lower_tag_name: "v2.0"
+  target: "main"
+  title: "v2.0"
+  sha1: "7197b56fdc75b453f47c9110938cb46a303579fd"
+  num_commits: 6
+  is_draft: false
+  is_prerelease: false
+  is_tag: false
+  created_unix: 946684803

models/fixtures/repo_unit.yml

@@ -1,3 +1,4 @@
+# See models/unit/unit.go for the meaning of the type
 -
   id: 1
   repo_id: 1
@@ -575,3 +576,28 @@
   repo_id: 56
   type: 1
   created_unix: 946684810
+-
+  id: 85
+  repo_id: 57
+  type: 1
+  created_unix: 946684810
+-
+  id: 86
+  repo_id: 57
+  type: 2
+  created_unix: 946684810
+-
+  id: 87
+  repo_id: 57
+  type: 3
+  created_unix: 946684810
+-
+  id: 88
+  repo_id: 57
+  type: 4
+  created_unix: 946684810
+-
+  id: 89
+  repo_id: 57
+  type: 5
+  created_unix: 946684810

models/fixtures/repository.yml

@@ -1,3 +1,4 @@
+# don't forget to add fixtures in repo_unit.yml
 -
   id: 1
   owner_id: 2
@@ -1647,3 +1648,16 @@
   is_private: true
   status: 0
   num_issues: 0
+
+-
+  id: 57
+  owner_id: 2
+  owner_name: user2
+  lower_name: repo-release
+  name: repo-release
+  default_branch: main
+  is_empty: false
+  is_archived: false
+  is_private: false
+  status: 0
+  num_issues: 0

models/fixtures/user.yml

@@ -66,7 +66,7 @@
   num_followers: 2
   num_following: 1
   num_stars: 2
-  num_repos: 12
+  num_repos: 13
   num_teams: 0
   num_members: 0
   visibility: 0