build(deps): bump better-auth from 1.1.20 to 1.1.21 (#1)

Bumps [better-auth](https://github.com/better-auth/better-auth/tree/HEAD/packages/better-auth) from 1.1.20 to 1.1.21.
- [Release notes](https://github.com/better-auth/better-auth/releases)
- [Commits](https://github.com/better-auth/better-auth/commits/v1.1.21/packages/better-auth)

---
updated-dependencies:
- dependency-name: better-auth
  dependency-type: direct:production
...

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