chore: make renovate work on v13 forgejo (#9679)

v13 is going to be released soon, v12 is EOL in a few days.

Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/9679
Reviewed-by: Michael Kriese <michael.kriese@gmx.de>
Co-authored-by: Gusted <postmaster@gusted.xyz>
Co-committed-by: Gusted <postmaster@gusted.xyz>

renovate.json

@@ -9,7 +9,7 @@
   "baseBranchPatterns": [
     "$default",
     "/^v11\\.\\d+/forgejo$/",
-    "/^v12\\.\\d+/forgejo$/"
+    "/^v13\\.\\d+/forgejo$/"
   ],
   "postUpdateOptions": ["gomodTidy", "gomodUpdateImportPaths", "npmDedupe"],
   "prConcurrentLimit": 10,