修复CI的报错，在build demo apk之前先清理一下工程

Change-Id: I738cdbd2a74d98ab253dfdffc6f77bbe8469f306

Author: SundoggyNew

.github/workflows/debug.yml

@@ -92,6 +92,7 @@ jobs:
           rm -rf explorer/explorer-device-rtc/src/main/java/com/tencent/iot/explorer/device/common/stateflow/*
           sed -i 's#//xxx##g' explorer/explorer-device-rtc/build.gradle
           sed -i 's#//xxx##g' explorer/explorer-device-video/build.gradle
+          ./gradlew clean
           ./gradlew :explorer:device-android-demo:build
       - name: Archive the apks
         uses: actions/upload-artifact@v2

.github/workflows/release.yml

@@ -95,6 +95,7 @@ jobs:
           rm -rf explorer/explorer-device-rtc/src/main/java/com/tencent/iot/explorer/device/common/stateflow/*
           sed -i 's#//xxx##g' explorer/explorer-device-rtc/build.gradle
           sed -i 's#//xxx##g' explorer/explorer-device-video/build.gradle
+          ./gradlew clean
           ./gradlew :explorer:device-android-demo:build
 #      - name: Archive the apks
 #        uses: actions/upload-artifact@v2