Fix for issue #5021 verifybamid2 module

[mmYeung]

PR checklist

updating input suffix check for reference file input, including nf-tests

Closes #5021

• [ x ] This comment contains a description of changes (with reason).
• [ x ] If you've fixed a bug or added code that should be tested, add tests!
• Ensure that the test works with either Docker / Singularity. Conda CI tests can be quite flaky:
  • For modules:
    • [ x ] nf-core modules test <MODULE> --profile singularity

[SPPearce]

@mmYeung , if you go to the github-invitations channel on the nf-core slack you can be added to the organisation, then the tests will run automatically.

[mmYeung]

Thanks @SPPearce, I've submitted a request on the Slack channel.

[SPPearce]

So one of the new files being generated is empty, which means that you have to explicitly change the nf-test assertion to only check for existence (else it is easy to accidentally assume the tool has worked properly when it is actually making empty files)