feat(private-key): escaped newlines will be replaced (#132)

via https://github.com/gr2m/universal-github-app-jwt/releases/tag/v2.1.1

tests/main-private-key-with-escaped-newlines.js

@@ -0,0 +1,6 @@
+import { test, DEFAULT_ENV } from "./main.js";
+
+// Verify `main` works correctly when `private-key` input has escaped newlines
+await test(() => {
+  process.env['INPUT_PRIVATE-KEY'] = DEFAULT_ENV.PRIVATE_KEY.replace(/\n/g, '\\n')
+});