[hotfix][python] Fix typo in PyFlink's JsonRowDeserializationSchema
[hotfix][python] Fix typo in PyFlink's JsonRowDeserializationSchema

This closes #20788.

apache/flink,wwjiang007/flink,wwjiang007/flink,apache/flink,apache/flink,zjureel/flink,apache/flink,lincoln-lil/flink,lincoln-lil/flink,zjureel/flink,lincoln-lil/flink,wwjiang007/flink,lincoln-lil/flink,wwjiang007/flink,lincoln-lil/flink,wwjiang007/flink,apache/flink,zjureel/flink,wwjiang007/flink,zjureel/flink,zjureel/flink,zjureel/flink,zjureel/flink,lincoln-lil/flink,lincoln-lil/flink,apache/flink,apache/flink,wwjiang007/flink