When EWS is rebasing, it needs a committer. By default, this will be the global git author, or, if that isn't set, some mangling of the machine name. This doesn't work on all machines, as seen in runs like this one: https://ews-build.webkit.org/#/builders/12/builds/73502. We should set this information via environment variables so it's consistent.
<rdar://problem/88967428>
Pull request: https://github.com/WebKit/WebKit/pull/146
Landed 247290@main (r289847)