Add reminder that pin must be in sync with two other places

cisagov/skeleton-generic, cisagov/skeleton-ansible-role, and
cisagov/skeleton-packer all must pin ansible-core and stay in sync.

requirements.txt

@@ -20,7 +20,11 @@ ansible>=8,<10
 # ansible/ansible#82702, which breaks any symlinked files in vars,
 # tasks, etc. for any Ansible role installed via ansible-galaxy.
 #
-# See also cisagov/skeleton-ansible-role#178.
+# See also cisagov/skeleton-ansible-role#178 and
+# cisagov/skeleton-generic#180.  Note from these PRs that any changes
+# made to this dependency must also be made in requirements-test.txt
+# in cisagov/skeleton-ansible-role and .pre-commit-config.yaml in
+# cisagov/skeleton-generic.
 ansible-core<2.16.3
 boto3
 docopt