Update dependabot to monitor github-actions (#379)

Author: damianszczepanik

.github/dependabot.yml

@@ -1,12 +1,20 @@
 # configuration: https://docs.github.com/en/code-security/dependabot/dependabot-version-updates/configuration-options-for-the-dependabot.yml-file
 
 version: 2
+
 updates:
-- package-ecosystem: maven
-  directory: "/"
-  schedule:
-    interval: monthly
-  open-pull-requests-limit: 3
-  target-branch: master
-  commit-message:
-    prefix: "[dependency] "
+  - package-ecosystem: maven
+    directory: "/"
+    schedule:
+      interval: monthly
+    target-branch: master
+    commit-message:
+      prefix: "[dependency] "
+
+  - package-ecosystem: github-actions
+    directory: "/"
+    schedule:
+      interval: monthly
+    target-branch: master
+    commit-message:
+      prefix: "[dependency] "