[gardener] Consolidate Mac test expectations for 2 prerender protocol-handler tests.

This consolidates the Mac test expectations for two tests:
external/wpt/speculation-rules/prerender/protocol-handler-register.https.html
external/wpt/speculation-rules/prerender/protocol-handler-unregister.https.html

These tests were showing enough flaky failures on the Mac platforms
where they were not annotated to show up in the top flaky tests list for
Mac14-arm64.  They were also showing occasional timeouts on Mac12 and
Mac12-arm64, and the -register test was showing flaky unexpected passes
on Mac15 and Mac15-arm64.

This updates all the Mac expectations to [ Pass Timeout ].

Bug: 40288240, 405192517, 405243128, 406805472
Change-Id: Id692113846965e0c1dd1bfc5b7373a312682ebff
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7850217
Auto-Submit: David Baron <dbaron@chromium.org>
Commit-Queue: David Baron <dbaron@chromium.org>
Commit-Queue: rubber-stamper@appspot.gserviceaccount.com <rubber-stamper@appspot.gserviceaccount.com>
Bot-Commit: rubber-stamper@appspot.gserviceaccount.com <rubber-stamper@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/heads/main@{#1630611}