macOS 14 (and higher) unit test never start on CI

[BPerlakiH]

On CI we have the following problem:

Testing failed:
	Kiwix (13599) encountered an error (Test runner never began executing tests after launching)
Test session results, code coverage, and logs:
** TEST FAILED **

According to the doc, it's due to Apple Sandbox for macOS:
https://developer.apple.com/documentation/security/accessing-files-from-the-macos-app-sandbox

Also other projects were hitting the same problem:
flutter/flutter#149264

Solution:
Turn off sandbox for CI unit tests.