automake: Update to version 1.18.1

automake: Update to version 1.18.1

- Update from version 1.18 to 1.18.1
- Update of rootfile not required
- Changelog
    1.18.1
	* Bugs fixed
	  - Undo change to mdate-sh; once again, it does not look at
	    SOURCE_DATE_EPOCH. This change was a misunderstanding that causes
	    problems, not fixes, for reproducible builds.
	    (https://lists.gnu.org/archive/html/automake/2025-06/msg00021.html)
	  - Improve debuggability of installcheck failures. (bug#78850)

Signed-off-by: Adolf Belka <adolf.belka@ipfire.org>
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>