[PNG] TAG approval, next step is CR

Hello everyone,

We just received TAG approval
<https://github.com/w3ctag/design-reviews/issues/873>! Our next step (as I
understand it, please correct me if I'm wrong) is Candidate Recommendation.
I'll review the W3C Process Document
<https://www.w3.org/2023/Process-20230612/> to make sure we're in a good
position for upcoming publications.

For example, PNG was previously published before the patent exclusion step
existed. So this time around, that was our first step this time. Usually,
part of moving to CR is a patent exclusion period. I'll double check if we
need another or if the first was sufficient.

Congrats, everyone!