dependabot: Run in our evenings, reduce limit

So far the daily updates tend to run in our mornings between 7:00 and
8:00, which blocks our CI for a long time, and thus collides with
developers sending PRs. Move them to the evening instead, when they can
use the quiet bots time.

Also reduce the number of parallel PRs from 5 to 3. Parallel ones always
need to be rebased, and thus are very expensive. We still want to be
able to have a complicated PatternFly PR open for several days without
blocking other updates.

.github/dependabot.yml

@@ -4,6 +4,10 @@ updates:
     directory: "/"
     schedule:
       interval: "daily"
+      # run these when most of our developers don't work, don't DoS our CI over the day
+      time: "22:00"
+      timezone: "Europe/Berlin"
+    open-pull-requests-limit: 3
     commit-message:
       prefix: "[no-test]"
     labels: