test: mark test-http-client-response-timeout flaky

Refs: nodejs#43680

Author: tniessen

test/parallel/parallel.status

@@ -28,6 +28,8 @@ test-http-server-headers-timeout-keepalive: PASS,FLAKY
 test-http-server-request-timeout-keepalive: PASS,FLAKY
 # https://github.com/nodejs/node/issues/43465
 test-http-server-request-timeouts-mixed: PASS,FLAKY
+# https://github.com/nodejs/node/issues/43680
+test-http-client-response-timeout: PASS,FLAKY
 
 [$arch==arm || $arch==arm64]
 # https://github.com/nodejs/node/pull/31178