Only Alpine kernels use the vmlinuz-VARIANT naming scheme, postmarketOS kernel images are always called vmlinuz. Since we only use our own kernels now, we can completely get rid of the variable and always look for vmlinuz. [ci:skip-vercheck]: the checks can't handle bumping pkgver *and* pkgrel [ci:skip-build]: takes a long time and already built successfully in CI Part-of: <https://gitlab.postmarketos.org/postmarketOS/pmaports/-/merge_requests/7398>