CI: ignore master branch for push events

CI: ignore master branch for push events

Due to problem with migrating from master to main as the default branch
and downstream project still requiring the master branch to be present,
we currently have for push events double CI runs, one for main and one
for master. To solve this ignore any push event to the master branch for
every workflow that react on push events.

Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>