github: Use Dependabot to keep Actions updated (#504)

Author: ansgarm

.github/dependabot.yml

@@ -11,10 +11,7 @@ updates:
     directory: "/tools"
     schedule:
       interval: "daily"
-  # Dependabot only updates hashicorp GHAs, external GHAs are managed by internal tooling (tsccr)
   - package-ecosystem: "github-actions"
     directory: "/"
     schedule:
       interval: "daily"
-    allow:
-      - dependency-name: "hashicorp/*"