use python-is-python3 (#1938)

Author: JasonGross

etc/ci/github-actions-docker-make.sh

@@ -14,7 +14,7 @@ sudo chmod -R a=u .
 git config --global --add safe.directory "*"
 echo '::group::install general dependencies'
 sudo apt-get update -y
-sudo apt-get install -y python python3 bsdmainutils ${EXTRA_PACKAGES}
+sudo apt-get install -y python-is-python3 python3 bsdmainutils ${EXTRA_PACKAGES}
 eval $(opam env)
 echo '::endgroup::'
 echo '::remove-matcher owner=coq-problem-matcher::'