doc: relocate doc for `share.safe-mismatch.source-safe.warn`

The documentation for the option is now right after its parent configuration:

  `share.safe-mismatch.source-safe`

Differential Revision: https://phab.mercurial-scm.org/D9837

mercurial/helptext/config.txt

@@ -1959,6 +1959,11 b' Alias definitions for revsets. See :hg:`'
     tries to upgrade the share; if it fails, continue by
     respecting the share source setting
 
+``safe-mismatch.source-safe.warn``
+    Shows a warning on operations if the shared repository does not use
+    share-safe, but the source repository does.
+    (default: True)
+
 ``safe-mismatch.source-not-safe``
 
     Controls what happens when the shared repository uses the share-safe
@@ -1977,12 +1982,6 b' Alias definitions for revsets. See :hg:`'
     tries to downgrade the share to not use share-safe;
     if it fails, continue by respecting the shared source setting
 
-
-``safe-mismatch.source-safe.warn``
-    Shows a warning on operations if the shared repository does not use
-    share-safe, but the source repository does.
-    (default: True)
-
 ``safe-mismatch.source-not-safe.warn``
     Shows a warning on operations if the shared repository uses share-safe,
     but the source repository does not.