Reduce codecov PR comments

Attempt to reduce the number of comments posted by codecov
to PR requests. Based on the codecov documenation setting
"require_changes=yes" and "behavior=once" should result in
a single comment under most circumstances.

https://docs.codecov.io/v4.3.6/docs/pull-request-comments

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #7022
Closes #7025