requirements: do not warn about dropping share-safe, unless explicitly set

If we are just altering the default value, this is "fine". This will get tested
once share-safe become the default.

Differential Revision: https://phab.mercurial-scm.org/D11994

mercurial/localrepo.py

@@ -3719,13 +3719,13 b' def checkrequirementscompat(ui, requirem'
             )
 
         if requirementsmod.SHARESAFE_REQUIREMENT in requirements:
-            ui.warn(
-                _(
+            if ui.hasconfig(b'format', b'use-share-safe'):
+                msg = _(
                     b"ignoring enabled 'format.use-share-safe' config because "
                     b"it is incompatible with disabled 'format.usestore'"
                     b" config\n"
                 )
-            )
+                ui.warn(msg)
             dropped.add(requirementsmod.SHARESAFE_REQUIREMENT)
 
     return dropped