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

META

@@ -6,5 +6,5 @@ Release:       1
 Release-Tags:  relext
 License:       CDDL
 Author:        OpenZFS
-Linux-Maximum: 6.3
+Linux-Maximum: 6.4
 Linux-Minimum: 3.10