build: fix MkDocs' Dockerfile base image tag (#266)

Author: Djaytan

docs/user-guide/Dockerfile

@@ -2,7 +2,7 @@
 # check=error=true
 
 # BusyBox command help: https://www.busybox.net/downloads/BusyBox.html
-FROM docker.io/python:3.13.14-alpine@sha256:b4d299311845147e7e47c970566906caf8378a1f04e5d3de65b5f2e834f8e3bf
+FROM docker.io/python:3.13.5-alpine@sha256:9b4929a72599b6c6389ece4ecbf415fd1355129f22bb92bb137eea098f05e975
 
 # Setup prerequisites for MkDocs Git-related features (e.g. revisions, collaborators, ...)
 RUN apk add --no-cache git