SCORU: inbox hashes are not hashed with the proper prefix

The following discussion from !5367 (merged) should be addressed:

• @yrg started a discussion: (+7 comments)

  To be precise, I think it is a SC_ROLLUP_COMMITMENT_HASH (as witnessed by the Co prefix).

Especially, the inbox hashes are actually those from Context_hash.t, which make them theorically undistinguishable from other generic hashes in the regression patterns (fortunately, there are not other generic hashes).