Use internal mirror for the laptop image.

CMK-33697

Change-Id: I8dd022c88baeeefa86c19fed3d456a49f96cbc44
(cherry picked from commit 488f4cf)

Author: nigelgbanks

buildscripts/infrastructure/build-nodes/laptops/Dockerfile

@@ -19,6 +19,8 @@ ENV \
 
 ARG ADDITIONAL_ARGS
 
+RUN sed -i "s|http://.*.ubuntu.com/ubuntu|http://apt.lan.checkmk.net/ubuntu|g" /etc/apt/sources.list.d/ubuntu.sources
+
 # used by install scripts
 COPY scripts/.bazelversion /opt/
 COPY scripts/defines.make /opt/