As Aakash pointed out, EWS machines restart pretty frequently, so they remove their temp directory. The issue with this is that check-github-mirror-integrity relies on the temp directory to store the svn.webkit.org cache.
<rdar://problem/81527357>
Created attachment 434925 [details] Patch
Comment on attachment 434925 [details] Patch rs=me
Created attachment 434929 [details] Patch
Committed r280663 (240269@main): <https://commits.webkit.org/240269@main> All reviewed patches have been landed. Closing bug and clearing flags on attachment 434929 [details].