fix: content encoding priorities

[shishir-karanth]

Checklist

• [x] run npm run test and npm run benchmark
• [x] tests and/or benchmarks are included
• [x] documentation is changed or added
• [x] commit message and code follows the Developer's Certification of Origin and the Code of conduct

[climba03003]

Can you add an unit test to ensure it works properly?

You can checkout the existing test inside https://github.com/fastify/fastify-compress/tree/master/test as example.