fix(ci): install bundler, remove dependabot config

.github/dependabot.yml

@@ -1,33 +0,0 @@
-version: 2
-updates:
-  - package-ecosystem: "github-actions"
-    directory: "/"
-    schedule:
-      interval: "weekly"
-      day: "monday"
-      time: "09:00"
-    groups:
-      github-actions:
-        patterns:
-          - "actions/*"
-          - "ruby/setup-ruby"
-          - "Homebrew/actions/*"
-    commit-message:
-      prefix: "ci"
-      include: "scope"
-
-  - package-ecosystem: "bundler"
-    directory: "/"
-    schedule:
-      interval: "weekly"
-      day: "monday"
-      time: "09:00"
-    groups:
-      development-dependencies:
-        dependency-type: "development"
-        patterns:
-          - "rubocop*"
-          - "rspec*"
-    commit-message:
-      prefix: "deps"
-      include: "scope"

.github/workflows/ci.yml

@@ -41,7 +41,9 @@ jobs:
         run: brew install-bundler-gems
 
       - name: Install project gems
-        run: bundle install
+        run: |
+          gem install bundler
+          bundle install
 
       - name: Run brew test-bot (cleanup)
         run: brew test-bot --only-cleanup-before