tests/sources/tar.py: `utils._force_rmtree` instead of giving 777 permissions
Description
This is part of #1220 - the linter really dislikes setting file permissions to 777
. This doesn't really matter in this case (we're deep in the test suite), but similar to !1744 (closed), there's not really a downside to changing it either.
Between this and !1744 (closed) all of the high severity issues would be resolved.
Edited by Tristan Maat