Configure Dependabot to check for updates daily

Dependabot is used to keep the project dependencies updated. Dependabot periodically checks for available updates, and
if found submits a pull request.

The frequency of the update checks is configurable. Despite the name, the "daily" schedule configuration previously used
actually only runs on weekdays. Maintenance of open source software projects is not necessarily limited to weekdays (and
in the case of volunteer projects, is more likely to occur on weekends). So the weekday-ly update checks tended to
result in a concentration of Dependabot pull requests on Mondays. This unnecessarily added to the busyness of an already
busy day.

Author: per1234

.github/dependabot.yml

@@ -11,15 +11,17 @@ updates:
       - per1234
     open-pull-requests-limit: 100
     schedule:
-      interval: daily
+      cronjob: 0 12 * * *
+      interval: cron
     labels:
       - "topic: infrastructure"
 
   - package-ecosystem: npm
     directory: /
     open-pull-requests-limit: 100
     schedule:
-      interval: daily
+      cronjob: 0 14 * * *
+      interval: cron
     labels:
       - "topic: infrastructure"
     assignees:
@@ -29,7 +31,8 @@ updates:
     directory: /
     open-pull-requests-limit: 100
     schedule:
-      interval: daily
+      cronjob: 0 15 * * *
+      interval: cron
     labels:
       - "topic: infrastructure"
     assignees: