action: reduce dependabot frequency from weekly to monthly, get rid of email spam (docsifyjs#2289)

Author: trusktr

.github/dependabot.yml

@@ -9,9 +9,19 @@ updates:
     directory: '/' # Location of package manifests
     open-pull-requests-limit: 10
     schedule:
-      interval: 'weekly'
+      interval: monthly
+    ignore:
+      # For all dependencies, trigger pull requests only for semver-major updates (ignore minor and patch).
+      - dependency-name: '*'
+        update-types:
+          ['version-update:semver-patch', 'version-update:semver-minor']
   - package-ecosystem: 'github-actions'
     directory: '/'
     open-pull-requests-limit: 10
     schedule:
       interval: monthly
+    ignore:
+      # For all dependencies, trigger pull requests only for semver-major and semver-minor updates (ignore patch).
+      - dependency-name: '*'
+        update-types:
+          ['version-update:semver-patch', 'version-update:semver-minor']