Bug 1800776 - Remove inline regex flags in .hgignore. r=firefox-build-system-reviewers,andi

Python 3.11 doesn't support those anymore.

Differential Revision: https://phabricator.services.mozilla.com/D162186

.hgignore

@@ -3,7 +3,8 @@
 # Filenames that should be ignored wherever they appear
 ~$
 \.py(c|o)$
-(?i)(^|/)TAGS$
+(^|/)TAGS$
+(^|/)tags$
 (^|/)ID$
 (^|/)\.DS_Store$
 \.pdb