Adjust the labels dependabot uses

Instead of using the default labels for the `github-actions` package
ecosystem we specify the labels explicitly. This is done to ensure that
dependabot uses our `github-actions` label instead of the default of
`github_actions`. We must also explicitly specify the `dependencies`
label since we are overriding the default label values.

Author: mcdonnnj

.github/dependabot.yml

@@ -21,6 +21,12 @@ updates:
     #   - dependency-name: hashicorp/setup-packer
     #   - dependency-name: hashicorp/setup-terraform
     #   - dependency-name: mxschmitt/action-tmate
+    labels:
+      # dependabot default we need to replicate
+      - dependencies
+      # This matches our label definition in .github/labels.yml as opposed to
+      # dependabot's default of `github_actions`.
+      - github-actions
     package-ecosystem: github-actions
     schedule:
       interval: weekly