kdump-cki: VMLINUZ_PATH should return only 1 value

Snippet of test failure

[  20:31:55  ] :: [  RUN  ] :: # /sbin/grubby --args="crashkernel=0G-4G:192M,4G-64G:192M,64G-1T:256M,1T-:512M" --update-kernel="/boot/vmlinuz-6.6.0
/boot/vmlinuz-6.6.0-61.fc40.s390x"
The param /boot/vmlinuz-6.6.0
/boot/vmlinuz-6.6.0-61.fc40.s390x is incorrect
[  20:31:55  ] :: [ ERROR ] :: Failed to update option: crashkernel=0G-4G:192M,4G-64G:192M,64G-1T:256M,1T-:512M on kernel /boot/vmlinuz-6.6.0
/boot/vmlinuz-6.6.0-61.fc40.s390x

Test logs on DataWarehouse

https://datawarehouse.cki-project.org/kcidb/tests/10137868

DataWarehouse issue

https://datawarehouse.cki-project.org/issue/2346

Additional details

https://gitlab.com/redhat/centos-stream/tests/kernel/kernel-tests/-/blob/main/kdump-cki/include/runtest.sh?ref_type=heads#L127

The problem happens, because the upstream kernel installed creates /boot/vmlinuz-6.6.0 while the the Fedora Rawhide kernel has similar version that creates /boot/vmlinuz-6.6.0-61.fc40.s390x

And the test ends up trying to pass both entries to --update-kernel parameter

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