fix(ci): free disk space before building debug androidTest APKs

The scheduled 'Run balances tests' workflow has been failing for weeks
with 'No space left on device' — assembleDebug + assembleDebugAndroidTest
for every module exceeds the ~14 GB free on GitHub-hosted runners.

Add an opt-in free-disk-space input to the reusable build workflow that
removes preinstalled toolchains we never use (dotnet, ghc, CodeQL, swift,
boost, etc., ~30+ GB), and enable it for the balances test build. Other
callers of the reusable workflow are unaffected.

.github/workflows/android_build.yml

@@ -31,6 +31,10 @@ on:
         required: false
         type: boolean
         default: false
+      free-disk-space:
+        required: false
+        type: boolean
+        default: false
     secrets:
       # Crowdloan secrets - NOT NEEDED for Pezkuwi (own blockchain)
       ACALA_PROD_AUTH_TOKEN:
@@ -140,6 +144,17 @@ jobs:
     runs-on: ubuntu-24.04
     timeout-minutes: 90
     steps:
+      - name: 🧹 Free disk space
+        if: ${{ inputs.free-disk-space }}
+        run: |
+          # The androidTest build of all modules fills the ~14 GB free on
+          # GitHub-hosted runners; drop preinstalled toolchains we never use.
+          sudo rm -rf /usr/share/dotnet /usr/share/swift /opt/ghc /usr/local/.ghcup \
+            /opt/hostedtoolcache/CodeQL /usr/local/share/boost /usr/local/share/powershell \
+            /usr/local/lib/node_modules /usr/local/julia* /opt/microsoft
+          sudo docker image prune -af > /dev/null 2>&1 || true
+          df -h /
+
       - name: Checkout particular branch
         uses: actions/checkout@v4
         with:

.github/workflows/balances_test.yml

@@ -14,6 +14,7 @@ jobs:
       upload-name: develop-apk
       run-tests: false
       build-debug-tests: true
+      free-disk-space: true
     secrets: inherit
 
   run-tests: