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 1d19423)

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

Author: miss-islington

Misc/NEWS.d/next/Tests/2023-02-11-20-28-08.gh-issue-89792.S-Y5BZ.rst

@@ -0,0 +1,3 @@
+``test_tools`` now copies up to 10x less source data to a temporary
+directory during the ``freeze`` test by ignoring git metadata and other
+artifacts.

Tools/freeze/test/freeze.py

@@ -80,7 +80,19 @@ def copy_source_tree(newroot, oldroot):
         if newroot == SRCDIR:
             raise Exception('this probably isn\'t what you wanted')
         shutil.rmtree(newroot)
-    shutil.copytree(oldroot, newroot)
+
+    def ignore_non_src(src, names):
+        """Turns what could be a 1000M copy into a 100M copy."""
+        # Don't copy the ~600M+ of needless git repo metadata.
+        # source only, ignore cached .pyc files.
+        subdirs_to_skip = {'.git', '__pycache__'}
+        if os.path.basename(src) == 'Doc':
+            # Another potential ~250M+ of non test related data.
+            subdirs_to_skip.add('build')
+            subdirs_to_skip.add('venv')
+        return subdirs_to_skip
+
+    shutil.copytree(oldroot, newroot, ignore=ignore_non_src)
     if os.path.exists(os.path.join(newroot, 'Makefile')):
         _run_quiet([MAKE, 'clean'], newroot)