Check for GitHub actions updates

Currently, `actions/checkout` is out-of-date, and uses a node version that has hit end-of-life. Dependabot should check new versions automatically, so that this won't be an issue.

Author: spenserblack

.github/dependabot.yml

@@ -0,0 +1,6 @@
+version: 2
+updates:
+  - package-ecosystem: github-actions
+    directory: "/"
+    schedule:
+      interval: "weekly"