Manually set cache directory path when running GUI tests

Author: GuillaumeGomez

src/ci/docker/host-x86_64/x86_64-gnu-tools/Dockerfile

@@ -101,5 +101,5 @@ COPY host-x86_64/dist-x86_64-linux/build-gccjit.sh /scripts/
 RUN /scripts/build-gccjit.sh /scripts
 
 ENV SCRIPT /tmp/checktools.sh ../x.py && \
-  NODE_PATH=`npm root -g` python3 ../x.py test tests/rustdoc-gui --stage 2 \
-    --test-args "'--no-sandbox --jobs 1'"
+  NODE_PATH=`npm root -g` PUPPETEER_CACHE_DIR="/root/.cache/puppeteer" python3 ../x.py \
+    test tests/rustdoc-gui --stage 2 --test-args "'--no-sandbox --jobs 1'"