poky-alt: switch preferred kernel to 6.12

6.6 is being removed from the upcoming LTS release, so we
adjust the alt config to use the 6.12 reference.

(From meta-yocto rev: 9502859f2d0c36d23cc23d3a91f1513eb748f0d3)

Signed-off-by: Bruce Ashfield <bruce.ashfield@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta-poky/conf/distro/include/poky-distro-alt-test-config.inc

@@ -2,7 +2,7 @@
 DISTRO_FEATURES:append = " pam usrmerge"
 
 # Use our alternate kernel version
-PREFERRED_VERSION_linux-yocto = "6.6%"
+PREFERRED_VERSION_linux-yocto = "6.12%"
 
 # Ensure the kernel nfs server is enabled
 KERNEL_FEATURES:append:pn-linux-yocto = " features/nfsd/nfsd-enable.scc"