upgrade: mark sharesafe improvement as only touching requirements

Upgrading the repository to use share safe functionality only touches
requirements.

Differential Revision: https://phab.mercurial-scm.org/D9772

mercurial/upgrade_utils/actions.py

@@ -291,6 +291,12 b' class sharesafe(requirementformatvariant'
         b' New shares will be created in safe mode.'
     )
 
+    # upgrade only needs to change the requirements
+    touches_filelogs = False
+    touches_manifests = False
+    touches_changelog = False
+    touches_requirements = True
+
 
 @registerformatvariant
 class sparserevlog(requirementformatvariant):