fix: explicitly pass platform to avoid docker InvalidBaseImagePlatfor…

[0xalpharush]

If I do not explicitly pass the platform on arm64 mac, I get the following error when running python3 infra/helper.py build_image tendermint:

- InvalidBaseImagePlatform: Base image gcr.io/oss-fuzz-base/base-builder-go was pulled with platform "linux/amd64", expected "linux/arm64" for current build (line 17)

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[0xalpharush]

Is there a way to sign the CLA without a gmail account?