fix: backend/Dockerfile to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-DEBIAN12-GLIBC-1547135
- https://snyk.io/vuln/SNYK-DEBIAN12-GLIBC-1547196
- https://snyk.io/vuln/SNYK-DEBIAN12-GNUTLS28-6062100
- https://snyk.io/vuln/SNYK-DEBIAN12-PERL-6085273
- https://snyk.io/vuln/SNYK-DEBIAN12-ZLIB-6008963

backend/Dockerfile

@@ -1,4 +1,4 @@
-FROM python:3.12-slim
+FROM python:3.13.0a2-slim
 
 ENV PYTHONFAULTHANDLER=1 \
   PYTHONUNBUFFERED=1 \