Add nf_core_version to .nf-core.yml

[Joon-Klaps]

#2741

PR checklist

• [X] This comment contains a description of changes (with reason)
• [x] CHANGELOG.md is updated
• [X] If you've fixed a bug or added code that should be tested, add tests!
• [ ] Documentation in docs is updated

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 0% with 5 lines in your changes are missing coverage. Please review.

Project coverage is 74.76%. Comparing base (2cb50ca) to head (099c01d).

:exclamation: Current head 099c01d differs from pull request most recent head 1fc8080. Consider uploading reports for the commit 1fc8080 to get more accurate results

Files	Patch %	Lines
nf_core/lint/nfcore_yml.py	0.00%	5 Missing :warning:

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[mashehu]

the AttributeError: 'called_once_with' is not a valid assertion. Use a spec for the mock if 'called_once_with' is meant to be an attribute.. Did you mean: 'assert_called_once_with'? errors are a known issue #2891, can be ignored for now