fix(ci): use github.token instead of secrets.GITHUB_TOKEN for gh CLI (#51)

## Summary
- Fixes release workflow failure by using `github.token` instead of
`secrets.GITHUB_TOKEN` for the `GH_TOKEN` environment variable in the
draft release creation step

## Root Cause
The GitHub CLI (`gh`) requires `GH_TOKEN` to be set to `github.token` in
GitHub Actions workflows. Using `secrets.GITHUB_TOKEN` caused the
workflow to fail with exit code 4:
```
gh: To use GitHub CLI in a GitHub Actions workflow, set the GH_TOKEN environment variable. Example:
  env:
    GH_TOKEN: ${{ github.token }}
```

## Test Plan
- [ ] Manually trigger the release workflow in a test run
- [ ] Verify the draft release is created successfully
- [ ] Confirm no exit code 4 errors

Fixes
https://github.com/pinecone-io/pinecone-mcp/actions/runs/21404698668

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> **Low Risk**
> Single-line CI/workflow change limited to GitHub release automation;
minimal blast radius outside the release job.
> 
> **Overview**
> Fixes the GitHub Actions release workflow by changing the `GH_TOKEN`
env var for the `gh release create` step from `secrets.GITHUB_TOKEN` to
`github.token`, preventing draft release creation failures during prod
releases.
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
2cefae0. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: jhamon

.github/workflows/release.yml

@@ -123,7 +123,7 @@ jobs:
         if: github.event.inputs.releaseMode == 'prod'
         shell: bash
         env:
-          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          GH_TOKEN: ${{ github.token }}
         run: |
           gh release create "v${{ steps.version-bump-prod.outputs.version }}" \
             --draft \