Backport !3891 - lib_protocol: use test stanza

Context

Changes in !3891 (merged) touch src/proto_alpha and we need them in snapshotted Protocol I. Cherry-picked all commits from it using the following commands.

$ git checkout -b proto-i-backport-3891
$ git cherry-pick e448365fb28cb96ef7d387ba77583f9462c4b8fc^..128ab791f6450f4452762504eaf61b53ed1a2fa7

Manually testing the MR

Check CI.