Add breaking change of new pandoc in release note

[cderv]

Relates to #13925 and jgm/pandoc#11409

This is adding a bullet in release note about this pandoc breaking change.

We don't usually do breaking change, and it is not ours, so I did not do it as a new ## Breaking section, but put it under the dependency itself.

Not sure about that though.

@cwickham what is your thought on that ?

This aimed to be in the doc.

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[cderv]

I see that my reported issue was fixed jgm/pandoc@d599154

so next Pandoc version will support ^[text]{.class} syntax. So maybe this is not worth adding anything ? And anyone encountering this will find the github issue about it ?

[cscheid]

I think we merge this, and when we get the upstream fix, then it will be a non-issue.