[10.x] Fixes validation rule format wheres method incorrectly `"NULL"` and `"NOT_NULL"` values as `null` and not `null`

[elminson]

This PR is to fix this issue https://github.com/laravel/framework/issues/49210

Added 2 test cases

cc: @driesvints

[taylorotwell]

Sorry, I'm not sure what we're fixing here and can't reproduce an issue locally.

The query is formatted correctly when it hits the database:

Please re-open with specific recreation instructions that actually cause a database issue if there is still a problem.

[driesvints]

@elminson are you still working on this? Did you see Taylor's questions?