Fix release_build

[jepio]

I tested the release process on a fork and there were issues:

• cri-o is missing releases for k8s 1.31 - skip
• nvidia-runtime needs to build with ubuntu 18 (not 20) because arm64 targets are missing
• needed to add cross-buildx to the workflow
• rke and k3s have '+' in filenames, this wasn't being handled correctly (asset urls contain an escape sequence)

[jepio]

This run illustrates the rke problem: https://github.com/jepio/sysext-bakery/actions/runs/10681647145/job/29607278902

These were the files for the previous release (i cleaned the invalid ones from the published release already):

https://github.com/flatcar/sysext-bakery/releases/download/latest/rke2-v1.29.2%2Brke2r1-arm64.raw
https://github.com/flatcar/sysext-bakery/releases/download/latest/rke2-v1.29.2%2Brke2r1-x86-64.raw
https://github.com/flatcar/sysext-bakery/releases/download/latest/rke2-v1.29.2.2Brke2r1-arm64.raw
https://github.com/flatcar/sysext-bakery/releases/download/latest/rke2-v1.29.2.2Brke2r1-x86-64.raw

and it failed when creating a new release:

Error: Failed to upload release asset rke2-v1.29.2%2Brke2r1-arm64.raw. received status code 404