[3.12] gh-124842: Fix test.support.import_helper.make_legacy_pyc() (GH-124843) (GH-124854)

For source file "path/to/file.py" it created file with incorrect path
"/absolute/path/to/path/to/file.pyc" instead of "path/to/file.pyc".
(cherry picked from commit 60ff67d010078eca15a74b1429caf779ac4f9c74)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>