[9.x] Fix QueryBuilder whereNot with array conditions

[Propaganistas]

$query->whereNot([
    'foo' => 1, 
    'bar' => 2
]);

currently yields not ( not foo = 1 and not bar = 2 )
while I would expect this to implictly become a nested clause not ( foo = 1 and bar = 2 ).

The commits in this PR are deliberately threefold:

1. the actual bugfix + tests
2. the consequence of reusing whereNested: aesthetically superfluous parentheses (but sql doesn't care).
3. a missing variable interpolation I encountered on the go

---

Note: the PR only tackles Query\Builder. The same principle probably applies for Eloquent\Builder

[BrandonSurowiec]

Since it has been like this for a long time this seems like a breaking change. Should probably target 10.x as someone out there is depending on the current behavior.

[rodrigopedra]

whereNot was introduced earlier this year by PR #41096.

I agree with @Propaganistas the expected behavior when passing an array should not be to negate it twice.

[taylorotwell]

Made the change only apply to arrays.