nixos/caddy: Fix string conversion for http and https ports (#507283)

          null

          options.services.caddy.httpPort.default

        ]

      ) "http_port ${cfg.httpPort}"}

      ) "http_port ${toString cfg.httpPort}"}

      ${optionalString (

        !elem cfg.httpsPort [

          null

          options.services.caddy.httpsPort.default

        ]

      ) "https_port ${cfg.httpsPort}"}

      ) "https_port ${toString cfg.httpsPort}"}

      log {

        ${cfg.logFormat}

      }