try a job to clean up disk space on runner, because now we get 'Syste…

…m.IO.IOException: No space left on device : '/home/runner/runners/2.311.0/_diag/Worker_...'

.github/workflows/run-unit-tests.yml

@@ -4,6 +4,26 @@ on:
   workflow_dispatch:
   pull_request:
 jobs:
+  free-disk-space:
+    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,
+        # if set to "true" but frees about 6 GB
+        tool-cache: false
+
+        # all of these default to true, but feel free to set to
+        # "false" if necessary for your workflow
+        android: true
+        dotnet: true
+        haskell: true
+        large-packages: true
+        docker-images: false
+        swap-storage: false
+
   docker-tests:
     name: "Run unit tests in docker"
     runs-on: ubuntu-latest