Update go-proxyproto library

What does this MR do?

Fixes: https://gitlab.com/gitlab-org/gitlab-pages/-/issues/699

• Update go-proxyproto library
• Fix test cases related to the update

https://github.com/pires/go-proxyproto/releases

TODO

• I added the Changelog trailer (e.g. Changelog: added) to the commits that need to be included in the changelog
• I added unit tests or they are not required
• I added acceptance tests or they are not required
• I added documentation (or it's not required)
• I followed code review guidelines
• I followed Go Style guidelines