manifestcache: do not display data when using --add

If the command invocation is about adding a new entry, we should remain terse
(the same as we do for many commands).

mercurial/debugcommands.py

@@ -1488,6 +1488,7 b' def debugmanifestfulltextcache(ui, repo,'
             except error.LookupError as e:
                 raise error.Abort(e, hint="Check your manifest node id")
             manifest.read()  # stores revisision in cache too
+            return
 
     cache = getcache()
     if not len(cache):

tests/test-manifest.t

@@ -111,9 +111,6 b' Showing the content of the caches after '
 Adding a new persistent entry in the cache
 
   $ hg debugmanifestfulltextcache --add 1e01206b1d2f72bd55f2a33fa8ccad74144825b7
-  cache contains 1 manifest entries, in order of most to least recent:
-  id: 1e01206b1d2f72bd55f2a33fa8ccad74144825b7, size 133 bytes
-  total cache data size 157 bytes, on-disk 157 bytes
 
   $ hg debugmanifestfulltextcache
   cache contains 1 manifest entries, in order of most to least recent: