chore(deps): bump python in /docker

Bumps python from 3.15.0a2-alpine3.22 to 3.15.0a3-alpine3.22.

---
updated-dependencies:
- dependency-name: python
  dependency-version: 3.15.0a3-alpine3.22
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

docker/Dockerfile

@@ -1,5 +1,5 @@
 # hadolint global ignore=DL3013,DL3018
-FROM --platform=$BUILDPLATFORM python:3.15.0a2-alpine3.22
+FROM --platform=$BUILDPLATFORM python:3.15.0a3-alpine3.22
 
 # For multi-platform build
 ARG BUILDPLATFORM