Fix buffer reuse for types.JSON fields

[shantanuraj]

• 8b2fd83 The test case is cherry picked from add TestBindJsonSlice #1426
• b5b94dd Fixes the buffer reuse
• 7f8daf0 Cleans up sliceType usage because bind doesn't need it anymore, drops a redundant err check.

We create a new instance of newStruct instead of reusing the previous oneStruct
Ensures memory is not shared between slice elements.

The tests from #1426 pass on this branch

go test github.com/aarondl/sqlboiler/v4/queries -run "TestBindJsonSlice"

Closes #1427