pickSHA: Improve pickSHA to handle pull_request_target and push

To support use in pull_request_target target workflows, we need to
use the pull_request.head.sha value for check-runs.

We also better support push target workflows by using the after
SHA value as it better represents "The SHA of the most recent commit on
ref after the push."

Signed-off-by: BJ Hargrave <bj@hargrave.dev>

src/main.ts

@@ -46,10 +46,15 @@ async function run(): Promise<void> {
 }
 
 function pickSHA(context: Context): string {
-  if (context.eventName === 'pull_request') {
-    return context.payload.pull_request?.head.sha || context.sha
+  switch (context.eventName) {
+    case 'pull_request':
+    case 'pull_request_target':
+      return context.payload.pull_request?.head.sha || context.sha
+    case 'push':
+      return context.payload.after || context.sha
+    default:
+      return context.sha
   }
-  return context.sha
 }
 
 run()