Context

The protocol PtMumbai is replaced by PtMumbai2 with Octez 16.0. Thus, the Mumbainet testnet has been relaunched with this new protoco.

This merge request updates the built-in alias --network mumbainet to match the new network TEZOS_MUMBAINET_2023-03-09T15:00:00Z.

Manually testing the MR

Run a node with --network mumbainet

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