bpo-37760: Mark all generated Unicode data headers as generated. (GH-15171)

This causes them to be collapsed by default in diffs shown on GitHub. https://bugs.python.org/issue37760 Automerge-Triggered-By: @benjaminp (cherry picked from commit 4e3dfcc) Co-authored-by: Greg Price <gnprice@gmail.com>

Author: miss-islington