ci: run goreleaser without the runner's GOCACHEPROG

goreleaser runs several go builds at once; each spawns its own gobuildcache,
and they time out on its per-entry file locks while one holds the lock
across a slow S3 call ('failed to acquire lock: context deadline exceeded',
check-release on #997). Use Go's local cache for goreleaser.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Ma8eHhW59hLAJuLzBnLvUu

.gitea/workflows/goreleaser.yaml

@@ -27,4 +27,5 @@ jobs:
         run: |
           GITEA_TOKEN=$(cat "${RELEASE_TOKEN_FILE}")
           export GITEA_TOKEN
-          goreleaser release --clean
+          # Without GOCACHEPROG: parallel builds contend for gobuildcache's locks.
+          env -u GOCACHEPROG goreleaser release --clean