github: allow dependeabot to update github workflow actions

Github usually updates their actions once a while and then warns about a
node env getting deprecated in runs. Which is not super easily spotted
by a developer until it's too late, so let's like npm let dependabot
handle updating.

.github/dependabot.yml

@@ -21,3 +21,9 @@ updates:
       patternfly:
         patterns:
           - "@patternfly*"
+
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    open-pull-requests-limit: 3
+    schedule:
+      interval: "weekly"