ci: codecov: Run on all zephyrproject-rtos organisation repositories

This commit updates the codecov workflow to run on all forks under the
zephyrproject-rtos organisation.

The purpose of this is mainly to simplify the process of testing of this
workflow under the zephyr-testing repository.

Signed-off-by: Stephanos Ioannidis <root@stephanos.io>
(cherry picked from commit c1bd5a61)