Add lint test for merge markers

[KevinMenden]

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

Adds a lint test looking for merge markers.

Closes #321

[codecov]

Codecov Report

Merging #861 (3982b11) into dev (bdba529) will decrease coverage by 1.46%.
The diff coverage is 90.32%.

@@            Coverage Diff             @@
##              dev     #861      +/-   ##
==========================================
- Coverage   73.20%   71.73%   -1.47%     
==========================================
  Files          22       30       +8     
  Lines        2784     3386     +602     
==========================================
+ Hits         2038     2429     +391     
- Misses        746      957     +211     

Impacted Files	Coverage Δ
nf_core/lint/merge_markers.py	90.00% <90.00%> (ø)
nf_core/lint/__init__.py	79.82% <100.00%> (ø)
nf_core/modules.py	45.05% <0.00%> (-43.74%)	⬇️
nf_core/lint/schema_params.py	78.94% <0.00%> (-5.27%)	⬇️
nf_core/__main__.py	64.18% <0.00%> (-0.24%)	⬇️
nf_core/bump_version.py	85.93% <0.00%> (-0.22%)	⬇️
nf_core/lint/actions_awstest.py	83.33% <0.00%> (ø)
nf_core/__init__.py	100.00% <0.00%> (ø)
nf_core/lint/actions_awsfulltest.py	93.10% <0.00%> (ø)
... and 4 more

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[KevinMenden]

Accidentally made this PR against master (again 🤦 ) that's why the branch protection failed....

[ewels]

Hmm strange - the comment still seemed to reference the wrong repo name, which should have been fixed in #860

[ewels]

Ah wait, the PR is against master so I guess that’s where the test is from as well so will need to wait for the release for the fix to be active..

[KevinMenden]

Okay good was already wondering why the tests still fail after running again 🤔

[ewels]

I think this should trigger a failure, not just a warning (so that it blocks PR merges).

Also suggested adding a pass if there are no problems found.

Haven't actually tried running the code yet but it looks fine to me 👍🏻

[BarryDigby]

Hi guys, just letting you know that the test fails on .png images, see below:

 merge_markers: Merge marker '<<<<<<<' in ./docs/images/output/DESeq2_QC/circRNA/DESeq2_dispersion.png: �4¨W¯^Ú\Oqqñ�#G.]º���������SXXhiiùl³<<<<<<<==   #Gܸq#))éÑ£GÅÅŦ¦¦666666¯¿þºWïÞ½ÍÍÍ�[YtA… │

grep -R "<<<<<<<" docs/images/
Binary file docs/images/output/DESeq2_QC/circRNA/DESeq2_dispersion.png matches

[KevinMenden]

Thanks! Didn't see that one coming ... @ewels maybe omit anything that ends with .png , .jpg etc?
Might be generally useful to have a list of file endings that are ignored.