Add dependabot

Author: mwcraig

.github/dependabot.yml

@@ -0,0 +1,12 @@
+version: 2
+updates:
+# Maintain dependencies for GitHub Actions
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+    # Open update PRs in groups rather than one-by-one
+    groups:
+      actions:
+        patterns:
+          - "*"