Fix Android Example Tests (com-lihaoyi#4785)

The tests now run concurrently with workers,
therefore the `out.json` is separated per worker.

Pull request: com-lihaoyi#4785

Author: gamlerhart

example/android/javalib/1-hello-world/build.mill

@@ -108,7 +108,7 @@ object app extends AndroidAppModule {
 > ./mill show app.test
 ...compiling 2 Java source...
 
-> cat out/app/test/testForked.dest/out.json
+> cat out/app/test/testForked.dest/worker-0/out.json
 ["",[{"fullyQualifiedName":"com.helloworld.ExampleUnitTest.textSize_isCorrect","selector":"com.helloworld.ExampleUnitTest.textSize_isCorrect","duration":...,"status":"Success"}]]
 
 */

example/android/javalib/1-hello-world/ignoreErrorsOnCI

@@ -105,13 +105,13 @@ object app extends AndroidAppKotlinModule {
 
 /** Usage
 
-> ./mill show app.test
+> ./mill -j 1 show app.test
 ...Compiling 2 Kotlin sources...
 
-> cat out/app/test/testForked.dest/out.json
+> cat out/app/test/testForked.dest/worker-0/out.json
 ["",[...{"fullyQualifiedName":"com.helloworld.ExampleUnitTest.text_size_is_correct","selector":"com.helloworld.ExampleUnitTest.text_size_is_correct","duration":...,"status":"Success"}...]]
 
-> cat out/app/test/testForked.dest/out.json
+> cat out/app/test/testForked.dest/worker-0/out.json
 ["",[...{"fullyQualifiedName":"com.helloworld.ExampleUnitTestInKotlinDir.kotlin_dir_text_size_is_correct","selector":"com.helloworld.ExampleUnitTestInKotlinDir.kotlin_dir_text_size_is_correct","duration":...,"status":"Success"}...]]
 
 */