Do weekly dependabot checks (#4399)

After we added a pubspec.lock I think it makes sense to update it more often

.github/dependabot.yml

diff --git a/.github/dependabot.yml b/.github/dependabot.yml
index fdb170b..2199393 100644
--- a/.github/dependabot.yml
+++ b/.github/dependabot.yml
@@ -4,7 +4,7 @@
   - package-ecosystem: "pub"
     directory: "/"
     schedule:
-      interval: "monthly"
+      interval: "weekly"
 
   - package-ecosystem: github-actions
     directory: /