`DefaultRedisSerializationContextBuilder.string()` should assign param to `stringTuple` instead of `hashValueTuple`

[imzhoukunqiang]

Hi Team,

Below there is a code snippet from DefaultRedisSerializationContext ,line 130. The string() method assign param tuple to hashValueTuple, it should be assigned stringTuple I think.

		@Override
		public RedisSerializationContextBuilder<K, V> hashValue(SerializationPair<?> tuple) {

			Assert.notNull(tuple, "SerializationPair must not be null");

			this.hashValueTuple = tuple;
			return this;
		}

		@Override
		public RedisSerializationContextBuilder<K, V> string(SerializationPair<String> tuple) {

			Assert.notNull(tuple, "SerializationPair must not be null");
                        
			this.hashValueTuple = tuple;
			return this;
		}

[jxblum]

Hi @imzhoukunqiang - Yes, upon review, your assessment here seems correct. Thank you for catching this problem and contributing a fix, as well as the nice set of test cases. Much appreciated.

It appears, this problem stems back to the 2.7.x branch as well.

I will finish the review, polish this a bit and merge it!