When running in a snap context we need to filtering out all the SNAP_*
variables out there, but this is not enough, because it's also needed
to sanitize them by ensuring that no variable containing a path pointing
to a $SNAP folder is leaked there.
Otherwise we might have (for example) XDG_RUNTIME_DIRS containing a
"private" snap path, and that will be exposed to all the applications
that will be started from ghostty
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