gh-89792: Prevent test_tools from copying 1000M of "source" in freeze test (GH-101837)

Prevent test_tools from copying 1000M of "source"

It doesn't need a git repo, just the checkout.  We skip .git metadata, Doc/build, Doc/venv, and `__pycache__` subdirs, that developers often have in their clients to reduce the size of the source tree copy ten-fold.

This should significantly reduce IO and presumably time on buildbots during this long test.
(cherry picked from commit 1d194235e4d5981b5fea25c75318d61189103a58)

Co-authored-by: Gregory P. Smith <greg@krypto.org>