Add disk space cleanup step to CI workflow

Added a step to free disk space before running checks.

Author: florian-huber

.github/workflows/CI_first_code_checks.yml

@@ -10,11 +10,16 @@ on:
         default: ''
 
 jobs:
-
   first_check:
     name: first code check / python-3.13 / ubuntu-latest
     runs-on: ubuntu-latest
     steps:
+      - name: Free Disk Space (Ubuntu)
+        uses: jlumbroso/free-disk-space@main
+        with:
+          # this might remove tools that are actually needed,
+          # when set to "true" but frees about 6 GB
+          tool-cache: true
       - uses: actions/checkout@v4
       - name: Set up Python
         uses: actions/setup-python@v5