Add `/usr/lib/mutter-13` to default search paths

[vixalien]

It seems the path "/usr/lib64/mutter-" is included by default, but not "usr/lib/mutter-", which is where mutter's files are installed on alpine/postmarketOS

[JumpLink]

@vixalien Thank you for this feedback, I have added this search path to #162, which should be merged soon 👍