[ci] Add check that the generated sources are up-to-date

If there isn't already a CI check to ensure that the generated sources are "up-to-date", then let's add one. This will catch cases where we forget to rebuild and commit the generated sources. It will also help prove the integrity of the binary `bpf_*.o` files.

Start by locating the existing CI configuration and the command that generates the committed sources and bpf_*.o files. Run the generation step and compare its output with the repository contents; done means CI detects and reports any differences so stale generated sources cannot be merged.

Written by the indexing model from the issue text.