github/workflows: Free up disk space on zephyr workflow.

The zephyr builds take up quite a lot of space.

Signed-off-by: Damien George <damien@micropython.org>

.github/workflows/ports_zephyr.yml

@@ -20,6 +20,15 @@ jobs:
   build:
     runs-on: ubuntu-latest
     steps:
+    - uses: jlumbroso/free-disk-space@main
+      with:
+        # Only free up a few things so this step runs quickly.
+        android: false
+        dotnet: true
+        haskell: true
+        large-packages: false
+        docker-images: false
+        swap-storage: false
     - uses: actions/checkout@v4
     - name: Install packages
       run: source tools/ci.sh && ci_zephyr_setup