fix(tags): nesting broken if casing differed

Tags are case insensitive, and we forgot a mapping

caused by two parent tags with different 'v' casing

```
AK_Step1_v12
AK_Step1_V12
```

=>

```
#AK_Step1_v12::#Pixorize::03_Pharmacology::22_Cardiovascular_(New)::01_Ivabradine
#AK_Step1_V12::#Pixorize::03_Pharmacology::22_Cardiovascular_(New)::02_Nitroprusside
```

Which caused `02_Nitroprusside` to be a top level deck

Fixes 18481

Author: david-allison

AnkiDroid/src/main/java/com/ichi2/anki/dialogs/tags/TagsArrayAdapter.kt

@@ -354,6 +354,7 @@ class TagsArrayAdapter(
      *
      * @param expandTarget The target tag to expand. Do nothing if it is empty or not found.
      */
+    @NeedsTest("#18481 - case insensitivity")
     private fun buildTagTree(expandTarget: String) {
         // init mapping for newly added tags
         filteredList.forEach {
@@ -380,7 +381,7 @@ class TagsArrayAdapter(
         for (tag in filteredList) {
             // root will never be popped
             while (stack.size > 1) {
-                if (!tag.startsWith(stack.peek().tag + "::")) {
+                if (!tag.startsWith(stack.peek().tag + "::", ignoreCase = true)) {
                     stackPopAndPushUp()
                 } else {
                     break