fix: don't error if event is not push

Assert `commits` array exists only AFTER confirming that event is
`push`. If event is not `push`, print warning and exit 0.

src/index.js

@@ -17,6 +17,14 @@ try {
   const name = repo.repo;
   const octokit = getOctokit();
 
+  if (eventName !== "push") {
+    core.warning(`This action only works with "push" events`, {
+      title: `Unsupported Event "${eventName}"`,
+    });
+
+    process.exit(0);
+  }
+
   const commits = (() => {
     const ret = payload.commits;
     assert(ret !== undefined, 'missing "commits" field of event payload ');
@@ -33,14 +41,6 @@ try {
 
   /*** Begin Validation ***/
 
-  if (eventName !== "push") {
-    core.warning(`This action only works with "push" events`, {
-      title: `Unsupported Event "${eventName}"`,
-    });
-
-    process.exit(0);
-  }
-
   let issueNumber = core.getInput("issueNumber", {
     required: false,
     trimWhitespace: true,