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 <[email protected]>

Author: miss-islington

.gitattributes

@@ -54,7 +54,7 @@ Python/Python-ast.c         linguist-generated=true
 Include/opcode.h            linguist-generated=true
 Python/opcode_targets.h     linguist-generated=true
 Objects/typeslots.inc       linguist-generated=true
-Modules/unicodedata_db.h    linguist-generated=true
+*_db.h                      linguist-generated=true
 Doc/library/token-list.inc  linguist-generated=true
 Include/token.h             linguist-generated=true
 Lib/token.py                linguist-generated=true