fix: mask the installation token in logs (actions#28)

The runner will automatically mask GitHub token formats it recognizes,
but sometimes a new pattern rolls out before the runner is updated to
recognize it.

lib/main.js

@@ -52,6 +52,9 @@ export async function main(
     repositoryNames: [repo],
   });
 
+  // Register the token with the runner as a secret to ensure it is masked in logs
+  core.setSecret(authentication.token);
+
   core.setOutput("token", authentication.token);
 
   // Make token accessible to post function (so we can invalidate it)