Create dependabot.yml

Create dependabot.yml to enable dependabot version updates.
Allow dependabot to open pull requests automatically to update depended github actions.

See:
Settings (of this repository) > Code security and analysis > Dependabot > Dependabot version updates

Author: k-takata

.github/dependabot.yml

@@ -0,0 +1,11 @@
+# To get started with Dependabot version updates, you'll need to specify which
+# package ecosystems to update and where the package manifests are located.
+# Please see the documentation for all configuration options:
+# https://docs.github.com/github/administering-a-repository/configuration-options-for-dependency-updates
+
+version: 2
+updates:
+  - package-ecosystem: "github-actions" # See documentation for possible values
+    directory: "/" # Location of package manifests
+    schedule:
+      interval: "weekly"