Revert "fix: Consider merge commits for single commit validation (#127)"

This reverts commit 1b347f7.

Author: amannn

src/index.js

@@ -58,17 +58,7 @@ module.exports = async function run() {
             per_page: 2
           });
 
-          // GitHub does not count merge commits when deciding whether to use
-          // the PR title or a commit message for the squash commit message.
-          const nonMergeCommits = commits.filter(
-            (commit) => !commit.message.startsWith('Merge branch')
-          );
-
-          // If there is only one (non merge) commit present, GitHub will use
-          // that commit rather than the PR title for the title of a squash
-          // commit. To make sure a semantic title is used for the squash
-          // commit, we need to validate the commit title.
-          if (nonMergeCommits.length === 1) {
+          if (commits.length === 1) {
             try {
               await validatePrTitle(commits[0].commit.message, {
                 types,