Update Meshtastic Protobufs to v2.7.21

[github-actions]

Protobuf Update Available

A new version of Meshtastic protobufs has been released.

	Version
Current	v2.7.20
Latest	v2.7.21

Update Instructions

Run the following command to update:

./scripts/generate_protos.sh update

Or to update to a specific version:

./scripts/generate_protos.sh update v2.7.21

Release Notes

View the release notes at:
https://github.com/meshtastic/protobufs/releases/tag/v2.7.21

Checklist

• Update protobufs using the script above
• Review generated Dart code changes
• Test with a physical Meshtastic device
• Update any app code affected by protobuf changes
• Commit and push changes

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This issue was automatically created by the protobuf update checker.