fix(CI): disable compat tests with 0.12, 0.13

It's not expected that we remain compatible with versions that required exposing
`solution.ml`.

Author: AltGr

.github/workflows/build-and-test.yml

@@ -38,8 +38,8 @@ jobs:
       fail-fast: false
       matrix:
         server_image:
-          - 'ocamlsf/learn-ocaml:0.12'
-          - 'ocamlsf/learn-ocaml:0.13.0'
+          # - 'ocamlsf/learn-ocaml:0.12'
+          # - 'ocamlsf/learn-ocaml:0.13.0'
           - 'learn-ocaml'  # use learn-ocaml image built from master
     env:
       USE_CLIENT_IMAGE: 'true'