automake: omit 1s test in _AM_FILESYSTEM_TIMESTAMP_RESOLUTION, for speed.

automake: omit 1s test in _AM_FILESYSTEM_TIMESTAMP_RESOLUTION, for speed.

From https://lists.gnu.org/archive/html/automake/2024-06/msg00055.html
plus https://lists.gnu.org/archive/html/automake/2024-06/msg00054.html.

* m4/sanity.m4 (_AM_FILESYSTEM_TIMESTAMP_RESOLUTION): Don't test
whether 1 sec works; instead just accept the 2 sec delay in the
Automake test $sleep in exchange for not incurring the 2s delay of
running the test for all packages on 1s-resolution platforms.
Platforms that support subsecond mtimes will still use them.