gitlab: 13.5.1 -> 13.6.0

Changed ruby version to 2.7.x to match upstream.
Added a gem config for gitlab-pg_query as it tries to download a source
tarball during the build process.
Also removed a patch for gitaly that has become obsolete by upstream fix
[here](https://gitlab.com/gitlab-org/gitaly/-/commit/de04077c25cc23b001317d2efdf5a9ead0bc86b9).

pkgs/applications/version-management/gitlab/update.py

@@ -1,5 +1,5 @@
 #!/usr/bin/env nix-shell
-#! nix-shell -i python3 -p bundix bundler common-updater-scripts nix nix-prefetch-git python3 python3Packages.requests python3Packages.click python3Packages.click-log vgo2nix yarn2nix
+#! nix-shell -i python3 -p bundix bundler common-updater-scripts nix nix-universal-prefetch python3 python3Packages.requests python3Packages.click python3Packages.click-log vgo2nix yarn2nix
 
 import click
 import click_log
@@ -40,9 +40,7 @@ class GitLabRepo:
         return versions
 
     def get_git_hash(self, rev: str):
-        out = subprocess.check_output(['nix-prefetch-git', self.url, rev])
-        j = json.loads(out)
-        return j['sha256']
+        return subprocess.check_output(['nix-universal-prefetch', 'fetchFromGitLab', '--owner', self.owner, '--repo', self.repo, '--rev', rev]).decode('utf-8').strip()
 
     @staticmethod
     def rev2version(tag: str) -> str: