ci: set dependabot to monthly

Signed-off-by: Bradley Reynolds <bradley.reynolds@darbia.dev>

Author: shenanigansd

.github/dependabot.yaml

@@ -1,19 +1,11 @@
-# To get started with Dependabot version updates, you'll need to specify which
-# package ecosystems to update and where the package manifests are located.
-# Please see the documentation for all configuration options:
-# https://docs.github.com/github/administering-a-repository/configuration-options-for-dependency-updates
-
 version: 2
-
 updates:
   - package-ecosystem: "github-actions"
-    # Workflow files stored in the
-    # default location of `.github/workflows`
     directory: "/"
     schedule:
-      interval: "weekly"
+      interval: "monthly"
 
-  - package-ecosystem: "cargo" # See documentation for possible values
-    directory: "/" # Location of package manifests
+  - package-ecosystem: "cargo"
+    directory: "/"
     schedule:
-      interval: "weekly"
+      interval: "monthly"