bump to 2.8dev

[mirpedrol]

PR checklist

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

[codecov]

Codecov Report

Merging #2137 (a50d352) into dev (9e6b67f) will increase coverage by 0.01%.
The diff coverage is n/a.

❗ Current head a50d352 differs from pull request most recent head 6777abb. Consider uploading reports for the commit 6777abb to get more accurate results

@@            Coverage Diff             @@
##              dev    #2137      +/-   ##
==========================================
+ Coverage   71.42%   71.43%   +0.01%     
==========================================
  Files          77       77              
  Lines        8367     8367              
==========================================
+ Hits         5976     5977       +1     
+ Misses       2391     2390       -1     

Impacted Files	Coverage Δ
nf_core/lint/__init__.py	74.18% <0.00%> (+0.40%)	⬆️

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