Create grouped dependabot.yml (#843)

Co-authored-by: Sindre Sorhus <[email protected]>

.github/dependabot.yml

@@ -0,0 +1,18 @@
+version: 2
+updates:
+  - package-ecosystem: 'github-actions'
+    directory: '/'
+    schedule:
+      interval: 'weekly'
+    groups:
+      github-actions:
+        patterns:
+          - '*'
+  - package-ecosystem: 'npm'
+    directory: '/'
+    schedule:
+      interval: 'weekly'
+    versioning-strategy: 'increase-if-necessary'
+    groups:
+      development-dependencies:
+        dependency-type: 'development'