Fix elvis operator on non-nullable type warning

Signed-off-by: Graham <gpe@openrs2.org>

archive/src/main/kotlin/org/openrs2/archive/key/JsonKeyReader.kt

@@ -21,12 +21,12 @@ public class JsonKeyReader @Inject constructor(
             root.isArray -> {
                 for (entry in root) {
                     val key = entry["key"] ?: entry["keys"] ?: throw IOException("Missing 'key' or 'keys' field")
-                    keys += mapper.treeToValue<XteaKey>(key) ?: throw IOException("Key must be non-null")
+                    keys += mapper.treeToValue<XteaKey?>(key) ?: throw IOException("Key must be non-null")
                 }
             }
             root.isObject -> {
                 for (entry in root.fields()) {
-                    keys += mapper.treeToValue<XteaKey>(entry.value) ?: throw IOException("Key must be non-null")
+                    keys += mapper.treeToValue<XteaKey?>(entry.value) ?: throw IOException("Key must be non-null")
                 }
             }
             else -> throw IOException("Root element must be an array or object")