CI: ensure subxt bindings are up-to-date

[pepyakin]

Instead of generating subxt bindings during each build we pregenerate them and commit in-tree. However, the bindings may go out-of-sync with the runtime due to (deliberate or accidential) changes.

Therefore, CI must fail for commits that have bindings that do not correspond to the bindings produces by a runtime should be marked as invalid.