chore: Add scheduled job to check for retrace spec changes

[romtsn]

Summary

• Adds a daily GHA workflow that checks if the upstream R8 retrace mapping spec (doc/retrace.md) has been updated
• Mirrors the approach from sentry-java#5157 for the tombstone proto schema
• Allows us to react to retrace format changes promptly

Test plan

• Verified the script runs successfully locally and reports "Spec is up to date"

🤖 Generated with Claude Code

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[Dav1dde]

Do you manually check the CI job output or is there some automatic alerting/intergration with slack?

[romtsn]

Do you manually check the CI job output or is there some automatic alerting/intergration with slack?

As i'm watching all activity on a repo I get notifications by email when a scheduled run fails on main, e.g.:

and here's the run (you can see it's triggered via schedule): https://github.com/getsentry/sentry-android-gradle-plugin/actions/runs/17966026056

[Dav1dde]

kk thanks, asking because we have a cron in Relay and I'd like to have it show up in Slack, was hoping maybe you have a trick for that!

[romtsn]

@Dav1dde pretty sure claude can build one in a breath via slackapi/slack-github-action but requires superpowers for a slack webhook and github repo secrets, which I don't have (probably only the latter for some repos)