Failure to unmarshal E2_HIGHCPU_32 machineType

Hi Team,

Similarly to what's been reported previously in #105, our notifier fails to unmarshal `E2_HIGHCPU_32` `machineType`:
```
notifiers.go:440] failed to unmarshal PubSub message id="" data="" publishTime="2022-08-26T19:31:45.596Z" into a Build: proto: (line 33:20): invalid value for enum type: "E2_HIGHCPU_32"
```
It seems that the associated [proto ](https://github.com/googleapis/go-genproto/blob/9e6da59bd2fcb05025546ef531505fa72c718e9b/googleapis/devtools/cloudbuild/v1/cloudbuild.pb.go#L661)already has it - so perhaps the proto package just need to be updated? Although the [go.mod version](https://github.com/GoogleCloudPlatform/cloud-build-notifiers/blob/20db36bb0171235ac1f1e7cb55b644621ea21ca4/go.mod#L25) seems to be later than the [one ](https://github.com/googleapis/go-genproto/commit/75c7a8546eb94f3738cbb05630843b11811d2866)where this machine type was added.

Thanks