fix: PR merge (#39442)

* Revert the behavior introduced by #30805
* Now the PR status is still managed in Gitea's code where the operation
is triggerred but not in post-receive hook
* Fix #39254 and many more related bugs.
    * Fix #39124

```
// MarkAsMerged sets a pull request to merged and closes the corresponding issue
// To make sure the pull request is marked as merged correctly, the caller uses multiple-stage operations:
//  1. Create a temp repo from base, merge the head into the temp repo, and get the merged commit ID and timestamp,
//  2. The merged commit ID and related information are stored into pull request
//  3. Push the merged commit to the base repo
//  4. Call MarkAsMerged to mark the pull request as merged and do post-processing (notification, close issues, etc)
//
// If failure occurs in step 1/2/3: the pull request is still open, the base repo is not changed, the doer can start a new merge.
// If failure occurs in step 4: the pull request can be marked as merged by the merged commit ID stored in it later.
```

services/pull/update.go

@@ -18,7 +18,6 @@ import (
 	"gitea.dev/modules/globallock"
 	"gitea.dev/modules/graceful"
 	"gitea.dev/modules/log"
-	"gitea.dev/modules/repository"
 )
 
 // Update updates pull request with base branch.
@@ -88,7 +87,7 @@ func Update(pr *issues_model.PullRequest, doer *user_model.User, message string,
 		BaseBranch: pr.HeadBranch,
 	}
 
-	_, err = doMergeAndPush(ctx, reversePR, doer, repo_model.MergeStyleMerge, "", message, repository.PushTriggerPRUpdateWithBase)
+	_, err = doMergeAndPush(ctx, reversePR, doer, repo_model.MergeStyleMerge, message, mergeAndPushOptions{})
 	// TODO: the "update" (merge target branch to PR head branch) operation has finished, there could still be some edge cases:
 	// * the database was already out of sync: the target branch was already in head branch:
 	//   * so no post-receive hook is really executed, no PR status update