generateContent: should return the aggregated response failed

This test failed! To configure my behavior, see [the Flaky Bot documentation](https://github.com/googleapis/repo-automation-bots/tree/main/packages/flakybot). If I'm commenting on this issue too often, add the `flakybot: quiet` label and I will stop commenting. --- commit: e9abf251d4802ccb6f5a72770baf5dd294c31cfd buildURL: [Build Status](https://source.cloud.google.com/results/invocations/37cb0624-ea9e-4b95-9afd-36a337a0efe9), [Sponge](http://sponge2/37cb0624-ea9e-4b95-9afd-36a337a0efe9) status: failed