fix: use startsWith() instead of exact match comparison

[andresmarpz]

• All new/changed/fixed functionality is covered by tests (or N/A)
• I have added documentation for all new/changed functionality (or N/A)

📋 Changes

Updates the checks from a strict equals condition to a startsWith(), since the URL could have trailing slash

📎 References

🎯 Testing

On the base v4 branch, boot up a test app and go to /auth/login, that should succeed. Then, on next.config.ts, set the config:

const config = {
  // ..more values
  trailingSlash: true
}

It won't work because an exact comparison won't be matched. It'll check /auth/login/ (the pathname on the middleware request) vs /auth/login (what's currently used as the hardcoded route on the mapping object).