fix: Drop container error to warning

[adamrtalbot]

Changes:

• Container registries do not have a consistent API, so calling them
  for container presence doesn't seem to work on GHCR or NVCR.
• In addition some registries require authentication and do not have a consistent method of authentication, likely oauth2 but not clear.
• This drops the error to a warning so we don't fail tests.

Relates to nf-core/modules#3693 and #2393

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 #2396 (c570b1d) into dev (9d63f93) will increase coverage by 0.02%.
The diff coverage is 50.00%.

@@            Coverage Diff             @@
##              dev    #2396      +/-   ##
==========================================
+ Coverage   71.12%   71.14%   +0.02%     
==========================================
  Files          87       87              
  Lines        9408     9410       +2     
==========================================
+ Hits         6691     6695       +4     
+ Misses       2717     2715       -2     

Files Changed	Coverage Δ
nf_core/modules/lint/main_nf.py	68.38% <50.00%> (+0.10%)	⬆️

... and 4 files with indirect coverage changes

[mirpedrol]

LGTM

[adamrtalbot]

You guys think this is OK? I wasn't sure if it was a good idea, but then again I don't see how to solve the container problem.

[mashehu]

yeah, it's a bit of cheating, but if it will not be too much to the point that we just start ignoring these warnings, it is fine.

[adamrtalbot]

Okey dokey, then let's goooo.