Update dependabot.yml

Revert back to a weekly schedule

Author: markwallace-microsoft

.github/dependabot.yml

@@ -9,8 +9,8 @@ updates:
   - package-ecosystem: "nuget"
     directory: "dotnet/"
     schedule:
-      interval: "cron"
-      cronjob: "0 8 * * 4,0" # Every Thursday(4) and Sunday(0) at 8:00 UTC
+      interval: "weekly"
+      day: "monday"
     ignore:
       # For all System.* and Microsoft.Extensions/Bcl.* packages, ignore all major version updates
       - dependency-name: "System.*"