feat: Check if the PR title matches the commit title when single comm…

…its are validated to avoid surprises (#158)

src/index.js

@@ -97,6 +97,14 @@ module.exports = async function run() {
                 `Pull request has only one commit and it's not semantic; this may lead to a non-semantic commit in the base branch (see https://github.community/t/how-to-change-the-default-squash-merge-commit-message/1155). Amend the commit message to match the pull request title, or add another commit.`
               );
             }
+
+            const commitTitle =
+              nonMergeCommits[0].commit.message.split('\n')[0];
+            if (commitTitle !== pullRequest.title) {
+              throw new Error(
+                `The pull request has only one (non-merge) commit and in this case Github will use it as the default commit message when merging. The pull request title doesn't match the commit though ("${pullRequest.title}" vs. "${commitTitle}"). Please update the pull request title accordingly to avoid surprises.`
+              );
+            }
           }
         }
       } catch (error) {