ci(build): Add packages:write permission to snapshot workflow (#3224)

## Summary

Fixes failed action here:
https://github.com/getsentry/sentry-cli/actions/runs/23303634015

- Adds `packages: write` to the snapshot workflow's top-level
permissions. GitHub validates reusable workflow permissions statically —
even though the docker jobs in `build.yml` have `if:
!inputs.is-snapshot` and won't run, the caller must still grant the
permissions they declare.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: runningcode

.github/workflows/snapshot.yml

@@ -6,6 +6,7 @@ on:
 
 permissions:
   contents: write
+  packages: write
 
 jobs:
   prepare: