utr: Print re-run warnings from the recipe as markdown

The recipe technically returns the summary of the build as markdown.
So the rerun warnings should probably be printed as such.

Today, a mismatch looks like:
https://screenshot.googleplex.com/4LWfvtAtmLek39o

With this and https://crrev.com/c/5408238, that becomes:
https://screenshot.googleplex.com/5G8E3r3kRfPcX7G

Bug: 41492688
Change-Id: I721c4fc903e76febf5b5df8ffda533b4581cac65
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5408259


Reviewed-by: Struan Shrimpton <sshrimp@google.com>
Commit-Queue: Ben Pastene <bpastene@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1280437}