dkms-autopkgtest: avoid catching packages with -no-dkms in their name

[Impact]

The current version of dkms-autopkgtest in 20.04 and later selects binary packages with names ending with "-dkms" for its automatic DKMS test. This also includes packages such as nvidia-headless-535-no-dkms, which are not real dkms packages, and should not be tested automatically by autopkgtest.

[Test Case]

Run autopkgtest in Focal, or later, for nvidia-graphics-drivers-535, and the test will fail because of nvidia-headless-535-no-dkms not being an actual dkms package.

https://kernel.ubuntu.com/adt-matrix/lunar-linux-meta.html

[Where problems could occur]

The main issue that we can experience is if the scripts dealt with other packages with "-no-dkms" in their name, which, for some reason, actually are DKMS packages, in which case, their testing would be skipped.