[9.x] Allow for int value parameters to whereMonth() and whereDay()

[lupinitylabs]

When trying to pass an integer value to whereMonth() or whereDay(), e.g.

User::whereMonth('updated_at', '=', 4)->get();

PHPstan will report Parameter #3 $value of method Illuminate\Database\Eloquent\Builder<App\Models\User>::whereMonth() expects DateTimeInterface|string|null, int given.

At the same time,

User::whereYear('updated_at', '=', 2022)->get();

will accept integer values.

This PR suggests to make the type definitions for whereYear(), whereMonth() and whereDay() more consistent by adding the int type to the @param docblock for $value.

I am swapping out the usage of str_pad() with sprintf() because the latter will accept mixed arguments, whereas for str_pad(), we would have to convert int values to strings first (and it's more compact, too).

[lupinitylabs]

Looks like the failing test is unrelated...?