ci: re-enable actions cache now that the runner serves it

The Gitea Actions cache service now answers on 10.200.0.1:43513
(post nftables fix on the runner side). Turn `cache: true` and
`cache: pnpm` back on so setup-go/setup-node can use it for
cross-job tarball caching on top of the host-persistent caches we
already rely on.

The setup-* actions still tolerate the cache being unavailable, so
this is reversible to `cache: false` if the service goes away again.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.gitea/workflows/integration.yaml

@@ -53,8 +53,7 @@ jobs:
         uses: actions/setup-go@v5
         with:
           go-version-file: go.work
-          # See go-unit.yaml for why `cache: true` is disabled.
-          cache: false
+          cache: true
 
       - name: Run integration suite
         # `make integration` precleans leftover docker-compose state and