fix: authenticate latest release lookup (#430)

## Summary

- Add an optional `github-token` input to authenticate the GitHub
release lookup used by `version: latest`.
- Pass the token through the composite action as
`SUPABASE_CLI_GITHUB_TOKEN` and use it as a bearer token for the
`/repos/supabase/cli/releases/latest` request.
- Update this repository's CI smoke test and README examples to pass
`${{ github.token }}` when testing or using `latest`.

## Root Cause

CI failed in `test (macos-latest, latest)` because the action resolved
`latest` through an unauthenticated GitHub REST API request and hit the
low unauthenticated rate limit. The dependency bump in #429 was not the
cause; the validate job passed and the failure happened inside the
release lookup path.

## Impact

Pinned versions continue to work without a token. For `version: latest`,
callers can now pass `${{ github.token }}` to avoid unauthenticated API
rate limiting while keeping the input optional for backward
compatibility.

## Validation

- `bun run ci`

.github/workflows/ci.yml

@@ -52,6 +52,7 @@ jobs:
       - uses: ./
         with:
           version: ${{ matrix.version }}
+          github-token: ${{ github.token }}
       - run: supabase -h
 
   ci: