more anki not building when local_backend is set

this is related but different enough to #671.

this happens after doing the local maven thing mentioned in #671.

```
> Task :libanki:testutils:compileDebugKotlin FAILED
e: file:///home/jake/code/Anki-Android/libanki/testutils/src/main/java/com/ichi2/anki/libanki/testutils/AnkiTest.kt:150:45 Cannot access 'GeneratedMessageLite' which is a supertype of 'Notetype'. Check your module classpath for missing or conflicting dependencies.
e: file:///home/jake/code/Anki-Android/libanki/testutils/src/main/java/com/ichi2/anki/libanki/testutils/AnkiTest.kt:150:45 Cannot access 'MessageLiteOrBuilder' which is a supertype of 'Notetype'. Check your module classpath for missing or conflicting dependencies.
e: file:///home/jake/code/Anki-Android/libanki/testutils/src/main/java/com/ichi2/anki/libanki/testutils/AnkiTest.kt:154:15 Cannot access 'GeneratedMessageLite' which is a supertype of 'OpChangesWithId'. Check your module classpath for missing or conflicting dependencies.
e: file:///home/jake/code/Anki-Android/libanki/testutils/src/main/java/com/ichi2/anki/libanki/testutils/AnkiTest.kt:154:15 Cannot access 'MessageLiteOrBuilder' which is a supertype of 'OpChangesWithId'. Check your module classpath for missing or conflicting dependencies.
e: file:///home/jake/code/Anki-Android/libanki/testutils/src/main/java/com/ichi2/anki/libanki/testutils/InMemoryAnkiTest.kt:27:28 Unresolved reference 'testing'.
e: file:///home/jake/code/Anki-Android/libanki/testutils/src/main/java/com/ichi2/anki/libanki/testutils/InMemoryAnkiTest.kt:42:9 Unresolved reference 'RustBackendLoader'.
e: file:///home/jake/code/Anki-Android/libanki/testutils/src/main/java/com/ichi2/anki/libanki/testutils/ext/Collection.kt:45:45 Cannot access 'EnumLite' which is a supertype of 'StockNotetype.Kind'. Check your module classpath for missing or conflicting dependencies.
e: file:///home/jake/code/Anki-Android/libanki/testutils/src/main/java/com/ichi2/anki/libanki/testutils/ext/Collection.kt:46:5 Cannot access class 'ByteString'. Check your module classpath for missing or conflicting dependencies.
e: file:///home/jake/code/Anki-Android/libanki/testutils/src/main/java/com/ichi2/anki/libanki/testutils/ext/Collection.kt:46:36 Cannot access class 'ByteString'. Check your module classpath for missing or conflicting dependencies.
```
it appears that rsdroid-testing is not getting linked (specifically the `Unresolved reference 'testing'.` part) and I'm just assuming the protobuf stuff is a side effect of that?