github: downgrade require_linked_github_account to warning

Some contributors still submit patches via the mailing list or are
not using GitHub entirely, so an unlinked commit author email
should not be treated as a hard failure.

Signed-off-by: Josef Schlehofer <pepe.schlehofer@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/24320
Signed-off-by: Jonas Jelonek <jelonek.jonas@gmail.com>

.github/formalities.json

@@ -23,7 +23,7 @@
   "check_space_after_assignment": false,
   "check_makefile_indentation": false,
   "check_pkg_release": "warning",
-  "require_linked_github_account": true,
+  "require_linked_github_account": "warning",
   "enable_stale_bot": false,
   "enable_labeler_yml": true
 }