workflows: linux: Fix accumulation of debs

[lool]

Currently, builds are accumulated in the linux-latest dir and multiple
kernels are pulled in the image. Instead, upload each build to separate
directories and maintain a linux-latest symlink pointing at the latest
one.

[lool]

Actually I need to land this now as this is already breaking images when there are multiple kernels for the same version, see e.g. this build https://github.com/qualcomm-linux/qcom-deb-images/actions/runs/14749719999/job/41419292313:

'/fileserver-downloads/qcom-deb-images/linux-deb-latest/linux-image-6.15.0-rc3-g9d7a0577c9db_6.15.0~rc3-g9d7a0577c9db-1_arm64.deb' -> 'debos-recipes/local-debs/linux-image-6.15.0-rc3-g9d7a0577c9db_6.15.0~rc3-g9d7a0577c9db-1_arm64.deb'
'/fileserver-downloads/qcom-deb-images/linux-deb-latest/linux-image-6.15.0-rc4-gca91b9500108_6.15.0~rc4-gca91b9500108-1_arm64.deb' -> 'debos-recipes/local-debs/linux-image-6.15.0-rc4-gca91b9500108_6.15.0~rc4-gca91b9500108-1_arm64.deb'
'/fileserver-downloads/qcom-deb-images/linux-deb-latest/linux-image-6.15.0-rc4-gb6ea1680d0ac_6.15.0~rc4-gb6ea1680d0ac-1_arm64.deb' -> 'debos-recipes/local-debs/linux-image-6.15.0-rc4-gb6ea1680d0ac_6.15.0~rc4-gb6ea1680d0ac-1_arm64.deb'

[lool]

Feeling very dumb to have landed this myself with a typo: linux-latest instead of linux-deb-latest :-(