Add base_sha option to clj-lint-action.

[niyarin]

This PR adds the option of clj-lint-action.
Without this option, the second commit on the branch would not be able to take the diff.

[codecov]

Codecov Report

Merging #198 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #198   +/-   ##
=======================================
  Coverage   86.90%   86.90%           
=======================================
  Files          77       77           
  Lines        6246     6246           
  Branches      519      519           
=======================================
  Hits         5428     5428           
  Misses        299      299           
  Partials      519      519           

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[alumi]

I'm sorry if I misunderstood, but I guess github.event.pull_request.base.sha is more suitable for PR events since files eventually changed in a PR are more important than files changed in the last commit of a PR.

[niyarin]

Thank you for the pointing.
I changed the options for pull requests as well as push.

[alumi]

Hmm..
In https://github.com/chrovis/cljam/pull/198/checks?check_run_id=719698533, the github.event.before on a push event seems to refer to 0444810 which is a force-pushed obsolete commit 🤔

[niyarin]

For a non-master branch, I changed the action to pick up the changes from the beginning of the branch.
・Changed clj-lint-action to take a diff from the head of that branch when passing an empty commit sha.
・Changed lint.yml to take base_sha only for master.

[alumi]

LGTM 👍 Thanks for your quick response!

[yito88]

LGTM!
Thank you 👍