Use context parameter in models/git (#22367)

After #22362, we can feel free to use transactions without
`db.DefaultContext`.

And there are still lots of models using `db.DefaultContext`, I think we
should refactor them carefully and one by one.

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

routers/web/repo/pull.go

@@ -659,7 +659,7 @@ func ViewPullCommits(ctx *context.Context) {
 	ctx.Data["Username"] = ctx.Repo.Owner.Name
 	ctx.Data["Reponame"] = ctx.Repo.Repository.Name
 
-	commits := git_model.ConvertFromGitCommit(prInfo.Commits, ctx.Repo.Repository)
+	commits := git_model.ConvertFromGitCommit(ctx, prInfo.Commits, ctx.Repo.Repository)
 	ctx.Data["Commits"] = commits
 	ctx.Data["CommitCount"] = len(commits)