Fix dependabot.yml handling

Need to ensure that this repository contains the superset of all
required values for all other repositories in the Homebrew GitHub
organisation so that filtering works as expected.

.github/actions/sync/shared-config.rb

@@ -73,6 +73,7 @@ def git(*args)
   ruby-macho
 ].freeze
 custom_dependabot_repos = %w[
+  .github
   brew
   ci-orchestrator
 ].freeze

.github/dependabot.yml

@@ -1,18 +1,55 @@
-# This file is synced from the `.github` repository, do not modify it directly.
----
+# This file is used as a base for all other repositories in the Homebrew GitHub
+# organisation so intentionally contains package-ecosystems that do not apply to
+# this repository.
 version: 2
+
 updates:
-- package-ecosystem: github-actions
-  directory: "/"
-  schedule:
-    interval: daily
-  allow:
-  - dependency-type: all
-  ignore:
-  - dependency-name: actions/stale
-  - dependency-name: dessant/lock-threads
-  groups:
-    artifacts:
-      patterns:
-      - actions/*-artifact
+  - package-ecosystem: github-actions
+    directory: /
+    schedule:
+      interval: daily
+    allow:
+      - dependency-type: all
+    # The actions in triage-issues.yml are updated in the Homebrew/.github repo
+    ignore:
+      - dependency-name: actions/stale
+      - dependency-name: dessant/lock-threads
+    groups:
+      artifacts:
+        patterns:
+          - actions/*-artifact
+
+  - package-ecosystem: bundler
+    directory: /
+    schedule:
+      interval: daily
+    allow:
+      - dependency-type: all
+
+  - package-ecosystem: npm
+    directory: /
+    schedule:
+      interval: daily
+    allow:
+      - dependency-type: all
+
+  - package-ecosystem: docker
+    directory: /
+    schedule:
+      interval: daily
+    allow:
+      - dependency-type: all
+
+  - package-ecosystem: devcontainers
+    directory: /
+    schedule:
+      interval: daily
+    allow:
+      - dependency-type: all
 
+  - package-ecosystem: pip
+    directory: /
+    schedule:
+      interval: daily
+    allow:
+      - dependency-type: all