Make testing and coding standards separate bullet points.

For the coding standards, add a "must", since some of it is now enforced on
the CI.

For tests, don't ask for "fully tested before submission": we don't expect
contributors to run all the tests locally. Ask for basic local testing, and
remind users to check CI results after submission.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>