Fix: update() parent pointers not updated after recursive merge with JSON_DIAGNOSTICS (#5187)

* added fix for issue 4813

Signed-off-by: VasuBhakt <cpswastik31@gmail.com>

* added regression test for 4813

Signed-off-by: VasuBhakt <cpswastik31@gmail.com>

* moved test from unit-regression2 to unit-diagnostics

Signed-off-by: VasuBhakt <cpswastik31@gmail.com>

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Signed-off-by: VasuBhakt <cpswastik31@gmail.com>