Linux 6.9 compat: META (openzfs#16358)

Update the META file to reflect compatibility with the 6.9
kernel.

Signed-off-by: Tony Hutter <[email protected]>
Reviewed-by: Brian Behlendorf <[email protected]>

Author: tonyhutter

META

@@ -6,5 +6,5 @@ Release:       1
 Release-Tags:  relext
 License:       CDDL
 Author:        OpenZFS
-Linux-Maximum: 6.8
+Linux-Maximum: 6.9
 Linux-Minimum: 3.10