fix: StackOverflowException in androidTest

Cause: `getDefaultAnkiDroidDirectory` caused recursion.
This recursion is normally gated on the existence of PREF_COLLECTION_PATH
But we didn't take this into account when in INSTRUMENTATION_TEST mode

This is fixed incidentally by 6dcf23fd10,
but the underlying cause wasn't handled

Tested by rebasing onto d88ad6251c
and running tests on `playDebug` (API 32 emulator)

Tests now fail due to an alternate setup issue

```
java.lang.NullPointerException
at com.ichi2.anki.TestUtils.isScreenSw600dp(TestUtils.kt:78)
at com.ichi2.anki.DeckPickerTest.checkIfStudyOptionsIsDisplayedOnTablet(DeckPickerTest.kt:91)
```

Fixes 13644

AnkiDroid/src/main/java/com/ichi2/anki/CollectionHelper.kt

@@ -544,8 +544,9 @@ open class CollectionHelper {
             return if (AnkiDroidApp.INSTRUMENTATION_TESTING) {
                 // create an "androidTest" directory inside the current collection directory which contains the test data
                 // "/AnkiDroid/androidTest" would be a new collection path
+                val currentCollectionDirectory = preferences.getOrSetString(PREF_COLLECTION_PATH) { getDefaultAnkiDroidDirectory(context) }
                 File(
-                    getDefaultAnkiDroidDirectory(context),
+                    currentCollectionDirectory,
                     "androidTest"
                 ).absolutePath
             } else if (ankiDroidDirectoryOverride != null) {