fix: Wrap an entrypoint by async to handle exceptions correctly (#363)

* fix: add return type

Co-authored-by: Shohei Ueda <30958501+peaceiris@users.noreply.github.com>

Author: yutopp

src/index.ts

@@ -1,8 +1,10 @@
 import * as core from '@actions/core';
 import * as main from './main';
 
-try {
-  main.run();
-} catch (e) {
-  core.setFailed(`Action failed with error ${e}`);
-}
+(async (): Promise<void> => {
+  try {
+    await main.run();
+  } catch (e) {
+    core.setFailed(`Action failed with error ${e.message}`);
+  }
+})();