Make token required for release-prep

Haven't figured out a way to securely provide this access automatically,
but it's not too arduous to require it of the action runner.

Author: reidmv

.github/workflows/release_prep.yml renamed to .github/workflows/release-prep.yml

@@ -5,7 +5,7 @@ on:
     inputs:
       personal_access_token:
         description: 'GitHub Personal Access Token'
-        required: false
+        required: true
 
 env:
   HONEYCOMB_WRITEKEY: 7f3c63a70eecc61d635917de46bea4e6