P4172 §11: switch from D4133 to P4133 once P4133 ships

[MungoG]

Mungo flagged in DM (2026-05-11 14:38):

4172-io-awaitables-design references 4133-proposal-
requirements. 4133 was deferred to July. The introduction to
section 11 in 4172 will need a bit of rework as it can't
reference an unpublished paper.

Vinnie's interim instruction (DM, 2026-05-11 14:39):

reference it as a d-paper

Current state: source/05-may/d4172-io-awaitables-design.md
Section 11 already cites D4133R0 as a D-paper (link
https://isocpp.org/files/papers/D4133R0.pdf), which satisfies
the interim direction.

Action:

1. When P4133 is published in a future mailing, swap the two
   D4133R0 references in P4172 (header of Section 11 and
   reference [40]) for the matching P4133R0 link
   (https://isocpp.org/files/papers/P4133R0.pdf /
   https://wg21.link/p4133).
2. Re-render the paper and bump P4172's revision in the next
   relevant mailing.
3. Close the issue.