update branch in CI and docs (#15631)

docs/content/doc/developers/migrations.en-us.md

@@ -20,7 +20,7 @@ repository data from other git host platforms to Gitea or, in the future, migrat
 git host platforms.  
 Currently, migrations from Github, Gitlab, and other Gitea instances are implemented.
 
-First of all, Gitea defines some standard objects in packages [modules/migrations/base](https://github.com/go-gitea/gitea/tree/master/modules/migrations/base).  
+First of all, Gitea defines some standard objects in packages [modules/migrations/base](https://github.com/go-gitea/gitea/tree/main/modules/migrations/base).  
 They are `Repository`, `Milestone`, `Release`, `ReleaseAsset`, `Label`, `Issue`, `Comment`, `PullRequest`, `Reaction`, `Review`, `ReviewComment`.
 
 ## Downloader Interfaces
@@ -31,11 +31,11 @@ To migrate from a new git host platform, there are two steps to be updated.
 - You should implement a `DownloaderFactory` which will be used to detect if the URL matches and create the above `Downloader`.
    - You'll need to register the `DownloaderFactory` via `RegisterDownloaderFactory` on `init()`.
 
-You can find these interfaces in [downloader.go](https://github.com/go-gitea/gitea/blob/master/modules/migrations/base/downloader.go).
+You can find these interfaces in [downloader.go](https://github.com/go-gitea/gitea/blob/main/modules/migrations/base/downloader.go).
 
 ## Uploader Interface
 
 Currently, only a `GiteaLocalUploader` is implemented, so we only save downloaded
 data via this `Uploader` to the local Gitea instance. Other uploaders are not supported at this time.
 
-You can find these interfaces in [uploader.go](https://github.com/go-gitea/gitea/blob/master/modules/migrations/base/uploader.go).
+You can find these interfaces in [uploader.go](https://github.com/go-gitea/gitea/blob/main/modules/migrations/base/uploader.go).