This uses github actions to synchronise `coverity-develop` to point at
`develop`, and so triggers a Coverity Scan build on a weekly basis, if
that branch has moved.
It is also possible to trigger this manually, by going to
https://github.com/eclipse/paho.mqtt.c/actions , selecting the
Synchronise Coverity Scan branches workflow, clicking `Run workflow`,
then `Run workflow`.
Signed-off-by: Roger A. Light <roger@atchoo.org>