fix: pass ACTIONS_CACHE_URL from Gitea variable to cache action

.github/actions/cache-dotnet/action.yml

@@ -5,6 +5,8 @@ runs:
   steps:
     - name: Cache NuGet packages
       uses: actions/cache@v4
+      env:
+        ACTIONS_CACHE_URL: ${{ vars.ACTIONS_CACHE_URL }}
       with:
         path: |
           ~/.nuget/packages