Add GITEA_PR_INDEX env variable to githooks (#35938)

`GITEA_PR_ID` is already part of the env variables available in the
githooks, but it contains a database ID instead of commonly used index
that is part of `owner/repo!index`

services/wiki/wiki.go

@@ -223,6 +223,7 @@ func updateWikiPage(ctx context.Context, doer *user_model.User, repo *repo_model
 			repo,
 			repo.Name+".wiki",
 			0,
+			0,
 		),
 	}); err != nil {
 		log.Error("Push failed: %v", err)
@@ -341,6 +342,7 @@ func DeleteWikiPage(ctx context.Context, doer *user_model.User, repo *repo_model
 			repo,
 			repo.Name+".wiki",
 			0,
+			0,
 		),
 	}); err != nil {
 		if git.IsErrPushOutOfDate(err) || git.IsErrPushRejected(err) {