fix update-nur-combined action for non-github/non-gitlab repos (#1035)

these were failing with `error: hash mismatch in fixed-output derivation`
messages, because `fetchgit` wasn't actually being passed any sha256.

see for example this run:
<https://github.com/nix-community/nur-combined/actions/runs/19902521411/job/57050064087#step:7:753>

fixes update for at least the following NUR repos:
- Pupyrinth (https://git.gliroid.com/Pupyrinth/nur-packages)
- alanpearce (https://git.alanpearce.eu/nix-packages)
- colinsane (https://git.uninsane.org/colin/nix-files)
- shelvacu (https://git.uninsane.org/shelvacu/nix-stuff)
- wolfangaukang (https://codeberg.org/wolfangaukang/nix-agordoj.git)

lib/repoSource.nix

@@ -45,7 +45,8 @@ else if (lib.hasPrefix "https://gitlab.com" attr.url || type == "gitlab") && !su
     inherit (revision) sha256;
   }
 else
-  fetchgit {
+  fetchgit (
+    {
       inherit (attr) url;
       inherit (revision) rev;
     }
@@ -58,3 +59,4 @@ else
           fetchSubmodules = submodules;
         }
     )
+  )