tests: Fix flaky MediaAccessTest.*

[magreenblatt]

To Reproduce
Steps to reproduce the behavior:

1. Run cefclient --gtest_filter=MediaAccessTest.* --use-views

Expected behavior
Tests should succeed. Instead, some tests fail.

On Windows:

[  FAILED  ] MediaAccessTest.DeviceSuccessAudioVideo
[  FAILED  ] MediaAccessTest.DeviceSuccessAudioVideoAsync
[  FAILED  ] MediaAccessTest.DesktopPartialSuccessReturningVideo

On MacOS:

[  FAILED  ] MediaAccessTest.DeviceSuccessAudioOnly
[  FAILED  ] MediaAccessTest.DeviceSuccessVideoOnly
[  FAILED  ] MediaAccessTest.DeviceSuccessAudioVideo
[  FAILED  ] MediaAccessTest.DeviceSuccessAudioVideoAsync
[  FAILED  ] MediaAccessTest.DesktopPartialSuccessReturningVideo

Sample failure:

[ RUN      ] MediaAccessTest.DeviceSuccessAudioOnly
../../cef/tests/ceftests/media_access_unittest.cc:255: Failure
Expected equality of these values:
  got_audio_device() || got_audio_desktop()
    Which is: true
  has_audio_access
    Which is: false
../../cef/tests/ceftests/media_access_unittest.cc:256: Failure
Value of: test_setup_->got_change
  Actual: true
Expected: false

Versions (please complete the following information):

• OS: Windows 11, MacOS 15.0.1
• CEF Version: M131