Bug 1793828 - Always print the reason why the site is not 'up-to-date' r=firefox-build-system-reviewers,nalexander

Previously most 'reasons' could only be seen if using a debugger, which
was not helpful when there was a problem in CI.

Depends on D158703

Differential Revision: https://phabricator.services.mozilla.com/D158704

python/mach/mach/site.py

@@ -552,6 +552,7 @@ class CommandSiteManager:
         """
         result = self._up_to_date()
         if not result.is_up_to_date:
+            print(f"Site not up-to-date reason: {result.reason}")
             active_site = MozSiteMetadata.from_runtime()
             if active_site.site_name == self._site_name:
                 print(result.reason, file=sys.stderr)