fix: case sensitive content type header in tests

Author: EsadCetiner

tests/regression/wordpress-rule-exclusions-plugin/9507350.yaml

@@ -31,7 +31,7 @@ tests:
               Host: localhost
               User-Agent: OWASP CRS test agent
               Accept: text/xml,application/xml,application/xhtml+xml,text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5
-              content-type: application/x-www-form-urlencoded
+              Content-Type: application/x-www-form-urlencoded
             port: 80
             method: POST
             version: "HTTP/1.1"