Incorrect header matching rules key in v2 pact files

[mefellows]

Sample (modified) but discovered by the V2 specs from the terraform client

{
  "consumer": {
    "name": "terraform-client"
  },
  "interactions": [
    {
      "description": "a request to create a system account",
      "request": {
        "method": "GET",
        "path": "/foo"
      },
      "response": {
        "matchingRules": {
          "$.header.Example": {
            "match": "type"
          }
        },
        "headers": {
          "Example": "value"
        },
        "status": 200
      }
    }
 ],
  "metadata": {
    "pactRust": {
      "ffi": "0.4.16",
      "mockserver": "1.2.5",
      "models": "1.1.19"
    },
    "pactSpecification": {
      "version": "2.0.0"
    }
  },
  "provider": {
    "name": "pactflow-application-saas"
  }
}

The field should be $.headers.<key> not $.header.<key> as per https://github.com/pact-foundation/pact-specification/blob/version-2/testcases/response/headers/matches%20with%20regex.json#L10.

[Saup21]

pact-foundation/pact-go#426

[rholshausen]

This has been around for a very long time. It was fixed in Pact-JVM in 2019 pact-foundation/pact-jvm#882