Make the test code compatible with -Wthread-safety

Make it clear to the compiler that gMutex is held while reading or
writing gReady.

Bug: 260725458
Change-Id: I197aca02c0e309c2c53b4e1995e9175b72109cb5
Signed-off-by: Bart Van Assche <bvanassche@google.com>
1 file changed