This is mainly to allow successful tests on CI/CD where we are running
as root. In practice is also a good idea to respect the permissions.
In real life installers make them r/w.
Files using macros can't be cached. Now if we find caches for them we
try to delete the caches (pypi installation for example). If we can't
remove the files a warning is generated.
If we fail to load a plug-in an error explaining it is generated.
Also added a test to reproduce it.
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