revert changes to workflow for container tests, stick to Ubuntu 18.04 there for now

Author: boegel

.github/workflows/container_tests.yml

@@ -3,10 +3,11 @@ name: Tests for container support
 on: [push, pull_request]
 jobs:
   build:
-    runs-on: ubuntu-22.04
+    # stick to Ubuntu 18.04, where we can still easily install yum via 'apt-get install'
+    runs-on: ubuntu-18.04
     strategy:
       matrix:
-        python: [3.7, 3.8, 3.9, '3.10']
+        python: [2.7, 3.6]
       fail-fast: false
     steps:
     - uses: actions/checkout@v2
@@ -23,7 +24,7 @@ jobs:
         sudo apt-get update -yqq
         # for building Singularity images
         sudo apt-get install rpm
-        sudo apt-get install dnf
+        sudo apt-get install yum
         # for modules tool
         sudo apt-get install lua5.2 liblua5.2-dev lua-filesystem lua-posix tcl tcl-dev
         # fix for lua-posix packaging issue, see https://bugs.launchpad.net/ubuntu/+source/lua-posix/+bug/1752082
@@ -84,11 +85,6 @@ jobs:
           # create $HOME/.rpmmacros, see also https://github.com/apptainer/singularity/issues/241
           echo '%_var /var' > $HOME/.rpmmacros
           echo '%_dbpath %{_var}/lib/rpm' >> $HOME/.rpmmacros
-          ls -ld $HOME/.rpmmacros
-          echo "contents of $HOME/.rpmmacros:"
-          cat $HOME/.rpmmacros
-          sudo echo '%_var /var' > /root/.rpmmacros
-          sudo echo '%_dbpath %{_var}/lib/rpm' >> /root/.rpmmacros
           # build CentOS 7 container image for bzip2 1.0.8 using EasyBuild;
           # see https://docs.easybuild.io/en/latest/Containers.html
           curl -OL https://raw.githubusercontent.com/easybuilders/easybuild-easyconfigs/develop/easybuild/easyconfigs/b/bzip2/bzip2-1.0.8.eb