Bug#1138999: mutter: frequent test failures on armhf

[Adrian Bunk]

Source: mutter
Version: 50~beta-2
Severity: serious
Tags: ftbfs
Control: block 1132301 by -1

https://buildd.debian.org/status/logs.php?pkg=mutter&arch=armhf

There is no clear pattern why/how it fails, but builds are
supposed to be non-flaky.