docker: Build arm image using ubuntu-24.04-arm runner

[anomiex]

Proposed changes:

Linux arm64 runners are in public preview. Building the arm64 part of the Docker image on one of these rather than in qemu should be a lot faster; let's try it.

Other information:

• Have you written new tests for your changes, if applicable?
• Have you checked the E2E test CI results, and verified that your changes do not break them?
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Jetpack product discussion

none

Does this pull request change what data or activity we track or use?

no

Testing instructions:

• See if the build worked and is faster.
• Try the image and see if it works.

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[tbradsha]

Seems to work for me (and ❤️ that build time).