fix: Remove invalid 'day' field from monthly schedule in dependabot.yml

- The 'day' field is not valid for monthly intervals in dependabot configuration
- Removed 'day: 1' from both gradle and github-actions update schedules
- This fixes the dependabot.yml validation errors in PRs

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: graycreate

.github/dependabot.yml

@@ -5,7 +5,6 @@ updates:
     directory: "/"
     schedule:
       interval: "monthly"
-      day: 1
       time: "09:00"
     open-pull-requests-limit: 10
     groups:
@@ -48,6 +47,5 @@ updates:
     directory: "/"
     schedule:
       interval: "monthly"
-      day: 1
       time: "09:00"
     open-pull-requests-limit: 5