cr-daily-branch: Actually use Linux 6.1 by default on Arm

cr-daily-branch: Actually use Linux 6.1 by default on Arm

Commit 95ee1714750b wasn't effective at changing the default version
of Linux, osstest kept on using "linux-arm-xen".

This time, make osstest use the same revision for both LINUX and
LINUX_ARM, like it was done for "linux*" branches only before.

If for some reason $BASE_TAG_LINUX and $BASE_TAG_LINUX_ARM are
different, this change would be wrong, but there's shouldn't be a need
for them to be different.

Fixes: 95ee1714750b ("ap-common: Switch to Linux 6.1 by default on Arm")
Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>