Add GHA for linting only the changes files

[IndrajeetPatil]

Closes #567

Changes from current version in {lintr}:

• Builds fail if any additional lints are found (which should also be the case in {lintr} once https://github.com/r-lib/lintr/pull/1522 is merged).
• Uses the .lintr file to find lintr settings instead of .lintr_new, which is something {lintr}-specific.

cc @MichaelChirico Do you see anything else that should be modified for general usage?

[codecov-commenter]

Codecov Report

Merging #620 (6f32ec2) into v2-branch (7dbac86) will not change coverage. The diff coverage is n/a.

@@             Coverage Diff             @@
##           v2-branch      #620   +/-   ##
===========================================
  Coverage     100.00%   100.00%           
===========================================
  Files              2         2           
  Lines             10        10           
===========================================
  Hits              10        10           

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[MichaelChirico]

Looks fine to me :)

[IndrajeetPatil]

@gaborcsardi Let me know if you need me to make any other changes here. Thanks.

[gaborcsardi]

Thanks! I am going to merge this now, but in the future we might move it to a different directory or repository, together with other "contributed" workflow examples, to make it clear that this does not have level of testing and support.

[github-actions[bot]]

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