ci: fix Restore tools step to use powershell shell for gitea-act runner

.gitea/workflows/ci.yml

@@ -48,6 +48,7 @@ jobs:
           Write-Host "NuGet cache hit: ${{ steps.nuget-cache.outputs.cache-hit }}"
 
       - name: Restore tools
+        shell: powershell
         run: dotnet tool restore
 
       - name: Restore
@@ -145,6 +146,7 @@ jobs:
           Write-Host "NuGet cache hit: ${{ steps.nuget-cache.outputs.cache-hit }}"
 
       - name: Restore tools
+        shell: powershell
         run: dotnet tool restore
 
       - name: Package with Velopack (Setup.exe + Portable.zip)