ci(docker): free disk space before image build to fix "no space left on device"

The docker-build and docker-compose-image-tag jobs intermittently fail with
"no space left on device". The docker-compose sanity check runs
`docker compose build superset-init`, which rebuilds the image from scratch
whenever the registry cache image (apache/superset-cache:<tag>) is missing -
and that uncached full rebuild exhausts the runner's ~14 GB root disk.

Reclaim the large preinstalled toolchains the build doesn't use (dotnet,
android, ghc, ghcup, CodeQL, boost) right after checkout, recovering ~20+ GB
of headroom. Plain shell step, no new action dependency.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

.github/workflows/docker.yml

@@ -75,6 +75,24 @@ jobs:
         with:
           persist-credentials: false
 
+      - name: Free up disk space
+        shell: bash
+        run: |
+          # Reclaim large preinstalled toolchains we don't use. The image
+          # build, and especially the docker-compose sanity check (which
+          # rebuilds from scratch whenever the registry cache image
+          # apache/superset-cache is unavailable), can otherwise exhaust the
+          # runner's root disk and fail with "no space left on device".
+          echo "Disk before cleanup:"; df -h /
+          sudo rm -rf \
+            /usr/share/dotnet \
+            /usr/local/lib/android \
+            /opt/ghc \
+            /usr/local/.ghcup \
+            /opt/hostedtoolcache/CodeQL \
+            /usr/local/share/boost || true
+          echo "Disk after cleanup:"; df -h /
+
       - name: Setup Docker Environment
         uses: ./.github/actions/setup-docker
         with:
@@ -148,6 +166,21 @@ jobs:
         uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6.0.3
         with:
           persist-credentials: false
+      - name: Free up disk space
+        shell: bash
+        run: |
+          # The sanity check rebuilds the image from scratch whenever the
+          # registry cache image apache/superset-cache is unavailable, which
+          # can exhaust the runner's root disk ("no space left on device").
+          echo "Disk before cleanup:"; df -h /
+          sudo rm -rf \
+            /usr/share/dotnet \
+            /usr/local/lib/android \
+            /opt/ghc \
+            /usr/local/.ghcup \
+            /opt/hostedtoolcache/CodeQL \
+            /usr/local/share/boost || true
+          echo "Disk after cleanup:"; df -h /
       - name: Setup Docker Environment
         uses: ./.github/actions/setup-docker
         with: