`unexpected operator` in conditional

[KmoM88]

On test-aptsource-pkg-install test, the conditional for legacy distros is not being evaluated and is giving false negatives.

On the last tag actions you can see unexpected operator in the test logs

  +test-aptsource-pkg-install | distro=ubuntu:focal repo=ros2
  +test-aptsource-pkg-install | --> RUN if [ "$legacy_distros" == *"$distro"* ]; then if grep 'BEGIN PGP PUBLIC KEY BLOCK' /usr/share/ros-apt-source/${repo}.sources > /dev/null ; then exit 0; else exit 1; fi; fi;
  +test-aptsource-pkg-install | /bin/sh: 1: [: ubuntu:focal debian:buster debian:bullseye: unexpected operator

This causes that for legacy distros that section of the test is being skipped.

I've tested modifying the conditional if with a case:

  RUN case "$legacy_distros" in \
    *"$distro"*) \
      echo "Distro legacy detected: $distro"; \
      if grep 'BEGIN PGP PUBLIC KEY BLOCK' /usr/share/ros-apt-source/${repo}.sources > /dev/null; then \
        exit 0; \
      else \
        exit 1; \
      fi \
      ;; \
    *) \
      echo "Distro not legacy: $distro. Skipping check."; \
      exit 0; \
      ;; \
  esac

But this gives me errors in the legacy distros (focal & buster) when the case is evaluated. I'll investigate further to validate that the PGP key is present in the file.