Use instanceof implicit casting

Co-authored-by: Martijn van Groningen <[email protected]>

Author: jordan-powers

modules/mapper-extras/src/main/java/org/elasticsearch/index/mapper/extras/MatchOnlyTextFieldMapper.java

@@ -379,8 +379,8 @@ public RowStrideReader rowStrideReader(LeafReaderContext context) throws IOExcep
 
                     @Override
                     protected BytesRef toBytesRef(Object v) {
-                        if (v instanceof BytesRef) {
-                            return (BytesRef) v;
+                        if (v instanceof BytesRef b) {
+                            return b;
                         } else {
                             return BlockSourceReader.toBytesRef(scratch, (String) v);
                         }