Fails to extract base commit on non-PR pushes.

[niyarin]

It doesn't seem to work when pushing directly to the main branch.
The causes seem to be as follows:

1. This line (

   clj-lint-action/entrypoint.sh

   Line 16 in 568db14

   BASE_NEXT_HASH=$(git log $BRANCH_NAME --not `git for-each-ref --format='%(refname)' refs |grep -v /$BRANCH_NAME$ ` --pretty=format:"%H"|tail -n 1)

   ) extracts the first commit that excludes commits only present in the branch to be merged.
2. This line is also executed when a commit is made directly to the main branch.

• One possible solution is to set BASE_NEXT_HASH to the previous commit if it's empty.
• Additionally, it might be worth updating the branch name check to include both master and main.