Linux 6.4 compat: META

Update the META file to reflect compatibility with the 6.4 kernel.

Reviewed-by: George Melikov <mail@gmelikov.ru>
Reviewed-by: Rob Norris <rob.norris@klarasystems.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #15095