Bump codecov/codecov-action from 3 to 4; explicitly pass the Codecov token; use the org-wide Codecov token; fail CI if the Codecov upload fails (so that we quickly notice if the Codecov uploads start having problems)

Bump codecov/codecov-action from 3 to 4; explicitly pass the Codecov token; use the org-wide Codecov token; fail CI if the Codecov upload fails (so that we quickly notice if the Codecov uploads start having problems) #56