ci: Bump f28-compose by 10 minutes

We're consistently seeing timeouts on the `f28-compose` test. It's
likely due to a performance regression in the backend rather than
anything else. I filed a ticket to get an investigation going, though
for now at least, let's bump the timeout some more to keep patches
flowing.

Closes: #1463
Approved by: jlebon

.papr.yml

@@ -109,7 +109,7 @@ context: f28-compose
 
 build: false
 
-timeout: 40m
+timeout: 50m
 
 required: true