Update Android Dockerfile to include root BUCK file (#31950)

Summary:
Pull Request resolved: #31950

Changelog: [Internal]

Adds the root BUCK file to the Docker image we use to test RNTester on CircleCI. See df9cd05

Reviewed By: ShikaSD

Differential Revision: D30099261

fbshipit-source-id: 936c505a0f4e7b791743901a06fa3b14c40b183e

.circleci/Dockerfiles/Dockerfile.android

@@ -25,6 +25,7 @@ ENV JAVA_TOOL_OPTIONS="-Dfile.encoding=UTF8"
 
 ADD .buckconfig /app/.buckconfig
 ADD .buckjavaargs /app/.buckjavaargs
+ADD BUCK /app/BUCK
 ADD Libraries /app/Libraries
 ADD ReactAndroid /app/ReactAndroid
 ADD ReactCommon /app/ReactCommon