ci: split assembleDebug and assembleBenchmark into separate gradle calls

Combining them into a single Gradle invocation caused
:amethyst:packagePlayBenchmark to fail inside AGP's
IncrementalSplitterRunnable worker — both variants share packaging
state in one task graph and the benchmark leg trips on it.

The old workflow always ran these as two separate `./gradlew` calls.
Match that pattern. They still run on the same runner with a warm
Gradle cache, so the compilation savings from sharing quartz/commons
with the test+packageDeb step are preserved; we only pay two Gradle
startups, which is trivial.

.github/workflows/build.yml

@@ -68,9 +68,13 @@ jobs:
       - name: Test + Build Desktop (gradle)
         run: ./gradlew test :desktopApp:${{ matrix.desktop-task }} --no-daemon
 
-      - name: Build Android APKs (gradle)
+      - name: Build Android Debug APKs (gradle)
         if: matrix.os == 'ubuntu-latest'
-        run: ./gradlew assembleDebug assembleBenchmark --no-daemon
+        run: ./gradlew assembleDebug --no-daemon
+
+      - name: Build Android Benchmark APKs (gradle)
+        if: matrix.os == 'ubuntu-latest'
+        run: ./gradlew assembleBenchmark --no-daemon
 
       - name: Android Test Report
         uses: asadmansr/android-test-report-action@v1.2.0