help: make the help for `safe-mismatch` real section

The extra new lines mean the minirst engine were not seeing them as section…
meaning they could not be addressed directly.

Differential Revision: https://phab.mercurial-scm.org/D12161

mercurial/helptext/config.txt

@@ -2029,7 +2029,6 b' Alias definitions for revsets. See :hg:`'
 ---------
 
 ``safe-mismatch.source-safe``
-
     Controls what happens when the shared repository does not use the
     share-safe mechanism but its source repository does.
 
@@ -2055,7 +2054,6 b' Alias definitions for revsets. See :hg:`'
     (default: True)
 
 ``safe-mismatch.source-not-safe``
-
     Controls what happens when the shared repository uses the share-safe
     mechanism but its source does not.