Add workspace pre-clean to avoid stale NFS handles on self-hosted runners

The actions/checkout clean step fails with ESTALE errors on NFS-backed
storage when build artifacts from previous runs have stale file handles.
Pre-clean with rm -rf (which tolerates stale handles) and disable
checkout's built-in clean.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: sbryngelson

.github/workflows/test.yml

@@ -199,8 +199,13 @@ jobs:
       ACTIONS_RUNNER_FORCE_ACTIONS_NODE_VERSION: node16
       ACTIONS_ALLOW_USE_UNSECURE_NODE_VERSION: true
     steps:
+      - name: Clean workspace
+        run: rm -rf "$GITHUB_WORKSPACE"/* "$GITHUB_WORKSPACE"/.[!.]* 2>/dev/null || true
+
       - name: Clone
         uses: actions/checkout@v4
+        with:
+          clean: false
 
       - name: Build
         if:   matrix.cluster != 'phoenix'