CameraXBasic sample test failing

Steps to reproduce:

1. Clone the repo
2. Open the CameraXBasic project
3. Run `./gradlew test`

Observe:

Build failure with the following output
```
> Task :app:testDebugUnitTest

com.android.example.cameraxbasic.MainInstrumentedTest > useAppContext FAILED
java.lang.NoClassDefFoundError at Shadows.java:2317
Caused by: java.lang.ClassNotFoundException at SandboxClassLoader.java:147
Caused by: java.lang.IllegalArgumentException at ClassReader.java:195

1 test completed, 1 failed

> Task :app:testDebugUnitTest FAILED

FAILURE: Build failed with an exception.

```

Environment info:
Android Studio Arctic Fox | 2020.3.1 Canary 12
Build #AI-203.7148.57.2031.7226969, built on March 22, 2021
Runtime version: 11.0.8+10-b944.6842174 x86_64
VM: OpenJDK 64-Bit Server VM by N/A
macOS 10.16
GC: G1 Young Generation, G1 Old Generation
Memory: 4096M
Cores: 8
Registry: external.system.auto.import.disabled=true, ide.images.show.chessboard=true
Non-Bundled Plugins: com.thoughtworks.gauge, com.developerphil.adbidea, com.google.mad-scorecard, org.intellij.plugins.markdown

Start in the CameraXBasic sample by running ./gradlew test and reproducing the app:testDebugUnitTest failure for MainInstrumentedTest.useAppContext. Trace the NoClassDefFoundError through the reported Shadows.java, SandboxClassLoader.java, and ClassReader.java locations; done means the test task completes successfully.

索引モデルが issue の本文から書いたものです。