[wpt-importer] Ensure rebaseline failures abandon the CL

Schedule `_ensure_cl_closed()` before `update_expectations_for_cl()` in
case the latter raises `ScriptError` when invoking `rebaseline-cl`. This
restores the behavior before crrev.com/c/5417478, although tests can no
longer check for `git cl set-close`.

Bug: 40631540
Change-Id: I62e86f0566a7ba53ae23e4a1634be52bd10ea85e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5426212


Reviewed-by: Weizhong Xia <weizhong@google.com>
Auto-Submit: Jonathan Lee <jonathanjlee@google.com>
Commit-Queue: Weizhong Xia <weizhong@google.com>
Cr-Commit-Position: refs/heads/main@{#1282778}