Fix Javadoc in ProtobufDecoder's MessageSizeReader API

Previously, the @⁠return tag in MessageSizeReader.readMessageSize() was
followed by a redundant "return", which rendered as "Returns: return
the message size..." in the published API documentation.

Closes gh-37079

Signed-off-by: BAE JAE HYEON <roblery128@gmail.com>

spring-web/src/main/java/org/springframework/http/codec/protobuf/ProtobufDecoder.java

@@ -299,7 +299,7 @@ public class ProtobufDecoder extends ProtobufCodecSupport implements Decoder<Mes
 		/**
 		 * Read the message size from the given buffer. This method may be
 		 * called multiple times before the message size is fully read.
-		 * @return return the message size, or {@code null} if the data in the
+		 * @return the message size, or {@code null} if the data in the
 		 * input buffer was insufficient
 		 */
 		@Nullable Integer readMessageSize(DataBuffer input);