Skip the test with 'pre' versions

Currently the ipykernel install step fails on the CI, see https://github.com/mwouts/jupytext/actions/runs/12338664239/job/34433965531

A similar report exists already at ipython/ipykernel#1292

.github/workflows/step_tests-pip.yml

@@ -29,10 +29,6 @@ jobs:
         python-version: [ "3.8", "3.9", "3.10", "3.11", "3.12", "3.13"]
         experimental: [false]
         include:
-          # Test pre-release versions
-          - python-version: "3.x"
-            dependency_type: "pre"
-            experimental: false
           # Test minimum markdown-it-py supported (otherwise the most recent version is used)
           - python-version: "3.x"
             markdown-it-py: "~=2.0"