chore(adapter): Update to better-auth 1.2.9

[cjroebuck]

Update better-auth to 1.2.9 (https://github.com/better-auth/better-auth/releases/tag/v1.2.9)

[changeset-bot]

⚠️ No Changeset found

Latest commit: 4fe32ee

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

Click here to learn what changesets are, and how to add one.

Click here if you're a maintainer who wants to add a changeset to this PR

[octet-stream]

I should probably bring dependabot or renvoate to manage to keep dependencies up to date for me :)