[gardener] Disable CanInspectAllowedHttpHost test.

The "DevToolsExtensionHostsPolicyTest.CanInspectAllowedHttpHost" test is
currently flaky across multiple Mac & Linux builders. As such, this CL
disables this test for these specific platforms.

The long-term goal should be to re-enable this test after we've
addressed the underlying source of flakiness.

Bug: 333791064
Change-Id: Id4f6ca25674c47caabe5d7a98405223dd13147ec
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5448238
Reviewed-by: Andrew Williams <awillia@google.com>
Owners-Override: Andrew Williams <awillia@google.com>
Auto-Submit: Khalid Peer <khalidpeer@chromium.org>
Commit-Queue: Khalid Peer <khalidpeer@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1286053}