CI: streamline caching in [ocaml-check]

What

Modification of [ocaml-check] job:

1. disable [cargo] and [sccache] caches.
2. set [dune] max cache size to 3 GB

Why

1. These caches are not used. (Cf. first commit's message for more info).
2. To reduce the risk of failure (OOMs, runner failure) and speed up the job.
   • Not entirely sure that this is the right value but we will monitor how it evolves.
   • There is a chance that the trimming does not work, ie the cache size will not be decreased. Again, we will monitor the situation.

How

• simple CIAO change + regenerate yaml files

Manually testing the MR

• make -C ci check passes
• cf. also some test pipelines in !18764 (closed).

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