dependabot: Group GitHub Actions updates (#169)

Since we look for these updates weekly, there will often be multiple. We
can group them to save work and manually handle splitting in the
hopefully rare cases it's needed.

.github/dependabot.yml

@@ -5,11 +5,18 @@ updates:
  schedule:
  interval: weekly
  open-pull-requests-limit: 5
+ groups:
+ actions:
+ update-types:
+ - minor
+ - patch
+
  - package-ecosystem: docker
  directory: /
  schedule:
  interval: weekly
  open-pull-requests-limit: 5
+
  - package-ecosystem: gomod
  directory: /
  schedule: