enable dependabot for GitHub actions (#220)

* enable dependabot for GitHub actions

* Reduce frequency

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Co-authored-by: David Widmann <[email protected]>

Author: ranocha

.github/dependabot.yml

@@ -0,0 +1,7 @@
+# https://docs.github.com/github/administering-a-repository/configuration-options-for-dependency-updates
+version: 2
+updates:
+  - package-ecosystem: "github-actions"
+    directory: "/" # Location of package manifests
+    schedule:
+      interval: "monthly"