fix dependabot.yml location

GitHub parses `dependabot.yml` as an action file because I put it in .github/workflows/ by mistake.
It should be `.github/dependabot.yml`.

See https://stackoverflow.com/questions/69446872/dependabot-error-githubl1-no-event-triggers-defined-in-on

.github/workflows/dependabot.yml

@@ -1,12 +0,0 @@
-# Set update schedule for GitHub Actions
-#
-# See https://docs.github.com/en/code-security/dependabot/working-with-dependabot/keeping-your-actions-up-to-date-with-dependabot
-
-version: 2
-updates:
-
-  - package-ecosystem: "github-actions"
-    directory: "/"
-    schedule:
-      # Check for updates to GitHub Actions every week
-      interval: "weekly"