Fix concurrency crash (#91)

Author: yizhengx

emulator/src/client/restful.go

@@ -50,8 +50,6 @@ func POST(service, endpoint string, port int, payload string, headers http.Heade
 
 	request, _ := http.NewRequest(http.MethodPost, url, bytes.NewReader(postData))
 
-	// Override the content type
-	headers.Set("Content-Type", "application/json")
 	// Forward any other headers set by the user
 	for key, values := range headers {
 		for _, value := range values {

emulator/src/stressors/forward.go

@@ -47,6 +47,9 @@ func ExtractHeaders(request any) http.Header {
 		}
 	}
 
+	// Override the content type
+	forwardHeaders.Set("Content-Type", "application/json")
+
 	return forwardHeaders
 }