Fix Sphinx markup.

Author: serhiy-storchaka

Doc/library/dbm.rst

@@ -237,7 +237,7 @@ functionality like crash tolerance.
       * ``'s'``: Synchronized mode.
         Changes to the database will be written immediately to the file.
       * ``'u'``: Do not lock database.
-      * ``'m'``: Do not use :man:`mmap(2)`.
+      * ``'m'``: Do not use :manpage:`mmap(2)`.
         This may harm performance, but improve crash tolerance.
         .. versionadded:: next
 

Doc/whatsnew/3.15.rst

@@ -93,7 +93,7 @@ dbm
 ---
 
 * Add the ``'m'`` flag for :func:`dbm.gnu.open` which allows to disable
-  the use of :man:`mmap(2)`.
+  the use of :manpage:`mmap(2)`.
   This may harm performance, but improve crash tolerance.
   (Contributed by Serhiy Storchaka in :gh:`66234`.)
 

Misc/NEWS.d/next/Library/2025-06-01-15-13-07.gh-issue-66234.Jw7OdC.rst

@@ -1,3 +1,3 @@
 Add the ``'m'`` flag for :func:`dbm.gnu.open` which allows to disable the
-use of :man:`mmap(2)`. This may harm performance, but improve crash
+use of :manpage:`mmap(2)`. This may harm performance, but improve crash
 tolerance.