Use post_password_required() for comment capability checks

[SergeyBiryukov]

[56836] introduced a few capability checks with ! empty( $post->post_password ).

Generally, we use post_password_required() for similar checks elsewhere in core.

Unless I'm missing something, it can be used here as well.

Follow-up to [56836], [57123].

[rajinsharwar]

Thank you for the patch @SergeyBiryukov. I guess we can get this reviewed and committed soon within this cycle. Marking this for commit.

[SergeyBiryukov]

This was fixed in [57285], the commit missed the ticket.