Reapply "format-code: fail on markdownlint warnings"

This reverts commit 6100d0bf6a0a30818a9508e344ea257df2574be6.

The reported issues were caused, not by markdownlint, but by a
upgrade of prettier that was not refreshed in all CI containers.

Change-Id: Ie5ec1849b5ee61cbfc5d376dfc14bf7a0aa1b89a
Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
1 file changed