chore(deps): bump python from 3.12-alpine to 3.13-alpine in /backend

Bumps python from 3.12-alpine to 3.13-alpine.

---
updated-dependencies:
- dependency-name: python
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

backend/Dockerfile

@@ -1,4 +1,4 @@
-FROM python:3.12-alpine AS base
+FROM python:3.13-alpine AS base
 
 RUN apk update --no-cache && apk upgrade --no-cache && apk add shadow --no-cache && useradd -m -r -u 1001 timed && apk del shadow && rm -rf /var/cache/apk/*