Fix copypasta error in casting

Signed-off-by: Peter Nied <[email protected]>

RFS/src/main/java/org/opensearch/migrations/bulkload/transformers/TransformerToIJsonTransformerAdapter.java

@@ -126,7 +126,7 @@ public GlobalMetadata transformGlobalMetadata(GlobalMetadata globalData) {
 
         var transformedLegacy = transformedTemplates.stream()
                 .filter(LegacyTemplate.class::isInstance)
-                .map(IndexTemplate.class::cast)
+                .map(LegacyTemplate.class::cast)
                 .collect(Collectors.toList());
 
         var transformedIndex = transformedTemplates.stream()