test: fall back to writable temp files for logs/status in /tmp (#6743)

A fixed /tmp path (log file, final heal status, warp log) can be owned by
another user on the shared runner (e.g. a previous root run), which made the
github-runner user fail: tee could not append the test log, the final heal
status write killed step 6 with EACCES, and upload-artifact could not read
stale root-owned warp logs. The heal scenario itself had passed
(summary=finished, vm002 reached the target) before the status-save died.

- Log files fall back to a unique mktemp path when the configured path is not
  writable (heal + pool scripts).
- The final heal status is written to a mktemp file (best effort).
- Workflow artifact uploads use globs for the fallback names.

.github/workflows/rustfs-pool-expand-test.yml

@@ -154,7 +154,7 @@ jobs:
         with:
           name: rustfs-pool-test-${{ github.run_id }}
           path: |
-            /tmp/rustfs-pool-test.log
+            /tmp/rustfs-pool-test*.log
             /tmp/rustfs-warp.*.log
           if-no-files-found: warn