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/go-unit.yaml

@@ -46,13 +46,7 @@ jobs:
         uses: actions/setup-go@v5
         with:
           go-version-file: go.work
-          # `cache: true` here pushes/pulls archives through the Gitea
-          # Actions cache service at 192.168.0.222:43513. That endpoint
-          # currently does not answer, and the action wastes minutes
-          # per run on reserveCache retries. In host-mode the real
-          # caches live in $HOME (~/go/pkg/mod, ~/.cache/go-build) and
-          # persist between jobs without any actions/cache plumbing.
-          cache: false
+          cache: true
 
       - name: Run Go tests
         # client/ is the deprecated Fyne client; excluded from CI per