ci: Build for both linux/amd64 and linux/arm64
Now that Blubber (and Kokkuri) support targeting multiple architectures and publishing under a single manifest index, let's publish versions that work on both linux/amd64 and linux/arm64.
Bug: T318866
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Now that Blubber (and Kokkuri) support targeting multiple architectures and publishing under a single manifest index, let's publish versions that work on both linux/amd64 and linux/arm64.
Bug: T318866