ci: run github-actions dependabot weekly on thursdays

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: wolpert

.github/dependabot.yml

@@ -54,6 +54,7 @@ updates:
     directory: "/"
     schedule:
       interval: "weekly"
+      day: "thursday"
     open-pull-requests-limit: 5
     commit-message:
       prefix: "ci"