Use sanitized snapshots for gcta/makegrmpart tests

[lyh970817]

PR checklist

• This comment contains a description of changes (with reason).
• If you've fixed a bug or added code that should be tested, add tests!
• If you've added a new tool - have you followed the module conventions in the contribution docs?
• If necessary, also make a PR on the nf-core/test-datasets repository.
• Make sure your code lints (nf-core modules lint gcta/makegrmpart).
• Ensure the test works with either Docker / Singularity. Conda CI tests can be quite slow; please only use them if you need them.

This updates the gcta/makegrmpart nf-test assertions to snapshot the sanitized full process.out object instead of manually snapshotting selected channels and versions. The updated snapshots now cover the complete emitted output contract for each successful test while keeping the tests simpler.

Tested with:

• nf-test test modules/nf-core/gcta/makegrmpart/tests/main.nf.test --profile=docker --update-snapshot --verbose