ci: add MCS to preprocess-deploy

[mbrcknl]

This commit will cause the preprocess-deploy workflow to fail if there
are changes to the preprocessed seL4 sources in MCS configurations
covered by the proofs. This means that changes to proof-relevant MCS
configurations will require a manual verification manifest update.

Previously, only non-MCS configurations were covered, which meant that
new verification manifests would be automatically deployed even if there
were proof-relevant changes to MCS code.

[mbrcknl]

Switching to draft while we think a bit more about seL4/l4v#497.

[axel-h]

This seem to copy what the preprocess step in https://github.com/seL4/seL4/blob/master/.github/workflows/pr.yml does already, right? Maybe this could be unified then?

[lsf37]

I don't think this can be unified, the MCS setup is a separate manifest and separate set of branches in the verification. It'll needs its own stream.

[lsf37]

Maybe I should phrase this differently: the current setup is already too unified and makes the assumption that in the verification the rt and master branches verify the same revision of the seL4 kernel. That assumption was fine before the C proofs started, but it is not true any more. Of course they should eventually converge and ideally remain at the same one, but that's the goal state, not the necessarily the current state.

[mbrcknl]

Closing for now. Will open new PRs when I have a proper solution to #497, i.e. automatic CPP-compatible updates in a separate stream for MCS.