Update to irmin.3.4.2

This MR aims to update the irmin dependency to 3.4.2.

Commit Context: use irmin.3.4.2 api uses the new API introduced. This commit might be useful for a wild opam repository update

Associated opam repo MR opam-repository!365 (merged)

TODO

• remove nomadic-lab repo target

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR