Fix compilation with gcc 13 and C++20

• updated Docker images
• add gcc "latest" builds and tests
• allow change of c++ standard version
• update Catch2 (fix build with gcc 13, #20 (closed))
• update nlohman json (fix build with C++20)

Closes #20 (closed)

tests/docker/Dockerfile-almalinux-8

-FROM almalinux:8
+FROM registry.cern.ch/docker.io/library/almalinux:8
 
 RUN dnf install -y 'dnf-command(config-manager)' epel-release && dnf config-manager --enable powertools \
  && dnf install -y \