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.

scripts/test/rustfs_pool_expand.sh

@@ -1128,6 +1128,12 @@ main() {
   trap 'rm -f "${ADMIN_API_CODE_FILE}"' EXIT
   if [ -n "${LOG_FILE}" ]; then
     mkdir -p "$(dirname "${LOG_FILE}")"
+    if ! touch "${LOG_FILE}" 2>/dev/null; then
+      # A fixed /tmp path may be owned by another user (e.g. a previous root
+      # run); fall back to a unique, always-writable temp file.
+      LOG_FILE="$(mktemp "${TMPDIR:-/tmp}/rustfs-pool-test.XXXXXX.log")"
+      warn "log file not writable; using ${LOG_FILE}"
+    fi
     exec > >(tee -a "${LOG_FILE}") 2>&1
   fi
   if [ "${RESET}" -eq 1 ]; then