Skip option does not work for pre-push hooks

[PidgeyBE]

🔧 Summary

The option to skip some hooks does not work correctly for pre-push hooks.
The check to determine if a branch is in merge state only works for pre-commit hooks.
One of the ways to check the state correctly for pre-push hooks is e.g. $(git log -1 --pretty=%P | wc -w) -gt 1.

Lefthook version

v1.7.15

Steps to reproduce

1. Have a pre-push hook that should be skipped for merge and rebase

pre-push:
  parallel: true
  commands:
    lint-yaml:
      glob: '*.{yml,yaml}'
      run: yamllint -d relaxed {push_files}
      skip:
        - merge
        - rebase

2. Check out a certain branch branch-x
3. Merge master, git merge master
4. Run pre-push hooks

Expected results

Because of skip: merge, the hook should be skipped

Actual results

The hook is not skipped.

Possible Solution

Instead of checking the presence of .git/MERGE_HEAD, in case of a pre-push hook, lefthook should check if the last commit was a merge commit or not. E.g. via $(git log -1 --pretty=%P | wc -w) -gt 1 in bash

[mrexox]

I will add a separate skip option merge-commit so you can use it instead of merge. I think this is more useful than supporting different behavior depending on the git hook name.