build(architecture): support pure JVM modules

fixes:

```
null cannot be cast to non-null type com.android.build.api.dsl.CommonExtension<*, *, *, *, *, *>
```

These may be useful in future, but not yet: Anki-Android-Backend is an
 Android module so we can't depend on it from pure JVM code

Author: david-allison

build.gradle.kts

@@ -41,9 +41,8 @@ subprojects {
     }
 
     afterEvaluate {
-        if (hasProperty("android")) {
-            val androidExtension =
-                extensions.findByName("android") as CommonExtension<*, *, *, *, *, *>
+        plugins.withType<com.android.build.gradle.BasePlugin> {
+            val androidExtension = extensions.getByName("android") as CommonExtension<*, *, *, *, *, *>
             androidExtension.testOptions.unitTests {
                 isIncludeAndroidResources = true
             }