Attempt to free disk space in CI for reproducible build check.

We were running out of disk space during the operation.
This attempts to remove some usused stuff to allow us to hopefully
complete the operation successfully.

.github/workflows/docker.yml

@@ -11,6 +11,11 @@ jobs:
   build:
     runs-on: ubuntu-latest
     steps:
+      - name: Free up disk space
+        run: |
+          sudo rm -rf /usr/share/dotnet /usr/local/lib/android/sdk/ndk /opt/ghc /usr/local/.ghcup /opt/hostedtoolcache/CodeQL
+          sudo docker image prune --all --force
+          df -h
       - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
         # gh api repos/actions/checkout/commits/v6 --jq '.sha'
       - name: Set up Docker Buildx