[GITEA] Allow release creation on commit

- The code and tests are already there to allow releases to be created
on commits.
- This patch modifies the web code to take into account that an commitID
could've been passed as target.
- Added unit test.
- Resolves https://codeberg.org/forgejo/forgejo/issues/1196

(cherry picked from commit 90863e0ab5)
(cherry picked from commit c805aa23b5)
(cherry picked from commit cf45567ca6)

routers/web/repo/release.go

@@ -387,7 +387,9 @@ func NewReleasePost(ctx *context.Context) {
 		return
 	}
 
-	if !ctx.Repo.GitRepo.IsBranchExist(form.Target) {
+	// form.Target can be a branch name or a full commitID.
+	if !ctx.Repo.GitRepo.IsBranchExist(form.Target) &&
+		len(form.Target) == git.SHAFullLength && !ctx.Repo.GitRepo.IsCommitExist(form.Target) {
 		ctx.RenderWithErr(ctx.Tr("form.target_branch_not_exist"), tplReleaseNew, &form)
 		return
 	}