Check CSP for background fetches
<rdar://problem/106025080>
Pull request: https://github.com/WebKit/WebKit/pull/10790
Submitted web-platform-tests pull request: https://github.com/web-platform-tests/wpt/pull/38741
Committed 261053@main (73c255a539a4): <https://commits.webkit.org/261053@main> Reviewed commits have been landed. Closing PR #10790 and removing active labels.