update nginx sslClientCertificatePath for client_ssl

When trying to run gitlab-qa Test::Integration::ClientSSL CE --no-test we were encountering an issue where the certs for nginx were being looked up from the incorrect place.

Updating the nginx config to point at the correct location allowing us to run this scenario manually. See https://gitlab.com/gitlab-org/gitlab/-/issues/331492#how-did-we-circumvent-this for further details