fix: docker/Dockerfile to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-DEBIAN12-AOM-7197979
- https://snyk.io/vuln/SNYK-DEBIAN12-GIT-6846203
- https://snyk.io/vuln/SNYK-DEBIAN12-GIT-6846203
- https://snyk.io/vuln/SNYK-DEBIAN12-KRB5-7411315
- https://snyk.io/vuln/SNYK-DEBIAN12-KRB5-7411315

docker/Dockerfile

@@ -13,7 +13,7 @@ RUN npm install npm@latest --location=global \
     && PUBLIC_URL=/static/reactapp/ npm run build
 
 # Stage 2: Backend
-FROM python:3.11.7 AS backend-build
+FROM python:3.14.0a4 AS backend-build
 
 ENV PYTHONUNBUFFERED 1
 ENV DJANGO_SETTINGS_MODULE threat_matrix.settings