fix warning

Author: breedx-splk

exporters/otlp/common/src/jmh/java/io/opentelemetry/exporter/internal/otlp/StringMarshalBenchmark.java

@@ -110,12 +110,12 @@ private static class TestMarshaler extends Marshaler {
       context = new MarshalerContext(/* marshalStringNoAllocation= */ true, useUnsafe);
     }
 
-    public void initialize(String string) {
+    private void initialize(String string) {
       value = string;
       size = StringAnyValueStatelessMarshaler.INSTANCE.getBinarySerializedSize(string, context);
     }
 
-    public void reset() {
+    private void reset() {
       context.reset();
     }