fix: avoid edge cases when identifying merge commits.

[neverendingqs]

There are ways to have a commit start with "Merge branch" even if it's not a merge commit:

• git commit -m "Merge branch ..."
• git cherry-pick -m 1 <hash>, where <hash> is a merge commit that starts with "Merge branch"
  • Functionally looks the same as the previous case
• git merge <hash> -m "Does not start with Merge branch"

By definition, merge commits are commits with more than one parent commit, so this should be a more robust way of identifying merge commits.

Quality notes:

• Functional:
  • Confirmed merge commits that do not begin with "Merge branch" do not count towards the commit count as expected
    • Before: feat: single commit followed by merge commit that does not start with "Merge branch" (before) neverendingqs-sandbox/test-repo-amannn-action-semantic-pull-request#9
    • After: feat: single commit followed by merge commit that does not start with "Merge branch" (after) neverendingqs-sandbox/test-repo-amannn-action-semantic-pull-request#10
  • Confirmed non-merge commits that begin with "Merge branch" does not count as a single-commit pull request as expected
    • Before: feat: single commit with non-semantic message. (before) neverendingqs-sandbox/test-repo-amannn-action-semantic-pull-request#7
    • After: feat: single commit with non-semantic message. (after) neverendingqs-sandbox/test-repo-amannn-action-semantic-pull-request#8

[wyardley]

Agree that the earlier logic is probably a bit simplistic. I had an action at a previous job configured to do essentially this; I forget the logic I used, but this seems sensible.

[amannn]

Thanks a lot for looking into this and your tests! This looks reasonable.

Can you however revert the changes to dist/index.js? This file is automatically built on master.

[github-actions]

🎉 This PR is included in version 3.4.6 🎉

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