Switch to Chrome for Testing and drop support for Chromium (#824)

We started installing Chromium because there is no linux ARM support
for Chrome yet. However, trying to run tests on Chromium seems to be
extra challenging. For example, upgrading to Debian 12 causes our
Javascript tests to fail on Chromium but not on Chrome.

Chrome for Testing was built specifically for web app testing so let's
follow Google's recommendation.

Author: tgxworld

image/discourse_test/Dockerfile

@@ -17,9 +17,7 @@ RUN chown -R discourse . &&\
 
 FROM base AS with_browsers
 
-ENV TESTEM_DEFAULT_BROWSER Chromium
-ADD install-chrome /tmp/install-chrome
-RUN /tmp/install-chrome &&\
+RUN npx @puppeteer/browsers install chrome@stable &&\
     apt update &&\
     apt install -y libgconf-2-4 libxss1 firefox-esr &&\
     cd /tmp && wget -q "https://download.mozilla.org/?product=firefox-latest-ssl&os=linux64&lang=en-US" -O firefox.tar.bz2 &&\