chore(deps): update docker updates (#3379)

This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [docker/dockerfile](https://redirect.github.com/moby/buildkit) |
syntax | minor | `1.9` -> `1.12` |
| python | final | minor | `3.12-slim` -> `3.13-slim` |

---

### Configuration

📅 **Schedule**: Branch creation - "* 0-3 1 * *" (UTC), Automerge - At
any time (no schedule defined).

🚦 **Automerge**: Disabled by config. Please merge this manually once you
are satisfied.

♻ **Rebasing**: Whenever PR becomes conflicted, or you tick the
rebase/retry checkbox.

👻 **Immortal**: This PR will be recreated if closed unmerged. Get
[config
help](https://redirect.github.com/renovatebot/renovate/discussions) if
that's undesired.

---

- [ ] <!-- rebase-check -->If you want to rebase/retry this PR, check
this box

---

This PR was generated by [Mend Renovate](https://mend.io/renovate/).
View the [repository job
log](https://developer.mend.io/github/marimo-team/marimo).

<!--renovate-debug:eyJjcmVhdGVkSW5WZXIiOiIzOS45Mi4wIiwidXBkYXRlZEluVmVyIjoiMzkuOTIuMCIsInRhcmdldEJyYW5jaCI6Im1haW4iLCJsYWJlbHMiOlsiZGVwZW5kZW5jaWVzIl19-->

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

docker/Dockerfile

@@ -1,5 +1,5 @@
-# syntax=docker/dockerfile:1.9
-FROM python:3.12-slim AS base
+# syntax=docker/dockerfile:1.12
+FROM python:3.13-slim AS base
 
 # Create a non-root user
 RUN useradd -m appuser