Update getQuery QueryObjectModelInterface method

[alexander-schranz]

I think there is not any case where getQuery can be null in this method.

[dbu]

looking at this code, i don't see how this could ever be nullable.

but this is not the right fix - we should remote the ? of getQuery.

very strictly speaking, this is a BC break if somebody overwrote that specific method, but i don't expect people to do that.

changing it in the annotation only is cheating on phpstan and could hide the problem rather than make people notice because of the conflict.

[alexander-schranz]

@dbu changed the native return type.