utils.py: Change permissions for rootpath in `_force_rmtree`

Description of the MR

As described in #912 (closed), extracting a tarball that has read-only permissions for ./ will change the permissions associated with the directory. This poses a problem if the directory it is extracted to is a tmp_dir which is intended to be deleted after extraction.

Proposed Changes

Get _force_rmtree to chmod +w the root directory.

This merge request, when approved, will close: #912 (closed)

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