ci: codecov: Use codecov/codecov-action@v3

This commit updates the CI workflows to use the codecov-action v3,
which is based on node.js 16 and @actions/core 1.10.0, in preparation
for the upcoming removal of the deprecated GitHub features.

Signed-off-by: Stephanos Ioannidis <root@stephanos.io>
(cherry picked from commit a982355f)