The previous code for the validator test was fairly messy due to
checking for both formats of the openapi url, one with
<variable_name> and the other with {variable_name}. To eliminate
this, we have standardized the format and restricted it to
{variable_name} as per the official format at:
https://swagger.io/docs/specification/describing-parameters.
When passing arguments with the `-d` syntax, which is convenient for
command-line examples, one needs to specify `-X GET` for curl to work
properly.
Fixes#12116