CI: Free disk space on Linux runners

Removing the Android toolchain saves 14 GiB, which gives us more room
for growth and to avoid running into out-of-space errors in the Linux
sanitizers + debug symbols builds.

Related to godotengine#79919, though the caches were just one part of the problem,
the real issue is that our Linux sanitizers builds take 12 GiB, and
adding godot-cpp on top with 2 GiB leaves only a few GiB left for the
cache itself.

.github/workflows/linux_builds.yml

@@ -85,6 +85,12 @@ jobs:
           sudo add-apt-repository ppa:kisak/kisak-mesa
           sudo apt-get install -qq mesa-vulkan-drivers
 
+      - name: Free disk space on runner
+        run: |
+          echo "Disk usage before:" && df -h
+          sudo rm -rf /usr/local/lib/android
+          echo "Disk usage after:" && df -h
+
       - name: Setup Godot build cache
         uses: ./.github/actions/godot-cache
         with: