Bug 1731282 [wpt PR 30785] - Fix endpoint URL for a COEP navigation reporting test...

Bug 1731282 [wpt PR 30785] - Fix endpoint URL for a COEP navigation reporting test so that it beco…, a=testonly

Automatic update from web-platform-tests
Fix endpoint URL for a COEP navigation reporting test so that it becomes runnable with WebKit test infrastructure (#30785)

The test was hardcoding `https://{{hosts[][www]}}:{{ports[https][0]}}/html/cross-origin-embedder-policy/resources/report.py`
for the endpoint URL. This resolved to `https://www.localhost:9443/html/cross-origin-embedder-policy/resources/report.py` but
the `https://www.localhost:9443` host is not supported by the WebKit layout test infrastructure (we only have
https://localhost:9443 & https://127.0.0.1:9443). To make the test runnable with the WebKit test infrastructure, I am updating
the headers file to use relative URLs for the endpoints.

I made a similar change for COOP tests in #30411.
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wpt-commits: 9b40f68b16e28a872213d9019f22904079170bdb
wpt-pr: 30785