Fix libc++ restarter job.

A while ago, the test workflow was updated with a new preemption regex,
however it was only applied to the test job, and not the job
that's actually restarting the failed libc++ test runs.

This fix should correct the issue and get the restarter working
again.

Author: EricWF

.github/workflows/libcxx-restart-preempted-jobs.yaml

@@ -33,7 +33,7 @@ jobs:
         with:
           script: |
             const failure_regex = /Process completed with exit code 1./
-            const preemption_regex = /The runner has received a shutdown signal/
+            const preemption_regex = /(The runner has received a shutdown signal)|(The operation was canceled)/
 
             const wf_run = context.payload.workflow_run
             core.notice(`Running on "${wf_run.display_title}" by @${wf_run.actor.login} (event: ${wf_run.event})\nWorkflow run URL: ${wf_run.html_url}`)