Update images to v2027.2.1

[crschardt]

Description

What changed?
This PR updates build.yml to use the v2027.2.1 custom images.

Why?

v2027.2.1 of the custom images includes Ubuntu 26.04 on RubikPi3 and Debian Trixie on the RK3588 (OrangePi5 & Rock-5c). These are the images that we hope to provide for 2027 season and this update supports testing them during the beta phase.

Testing

• I have tested this change locally
• Test evidence (screenshots, videos, or test results):

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Related Issues

Closes #

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AI Disclosure

• This PR was authored entirely by me
• This PR includes AI-generated code (e.g., from GitHub Copilot, ChatGPT)
  • If yes, I have reviewed all AI-generated code for correctness
  • If yes, please describe which parts were AI-assisted:

Describe AI involvement here if applicable

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Merge Checklist

• PR title is a short, imperative summary of changes
• PR description documents the what and why

Additional Checks (if applicable)

• User-facing changes? User documentation is updated
• Breaking changes? Migration guide is included in description and migrations are marked with // MIGRATION: <dataYear> where <dataYear> is the last season the pre-migration data was used in
• Bug fix? Regression test is added
• New dependency? License compatibility is verified and steps have been taken to follow it
• Serde changes? All messages are regenerated with no unexpected hash changes
• Configuration changes? Changes are backwards compatible with previous season's last release
• Pipeline/data exchange changes? Frontend types are updated in ./photon-client/src/types