fix(ci): restate RuboCop's default excludes alongside the e2e-cli one

An AllCops Exclude replaces the default list instead of extending it, so
adding e2e-cli silently un-excluded vendor/**, and RuboCop then loaded the
.rubocop.yml shipped inside a vendored gem, which requires a plugin this
project does not depend on.

Author: MichaelGHSeg

.rubocop.yml

@@ -5,6 +5,14 @@ AllCops:
   SuggestExtensions: false
   NewCops: disable
   Exclude:
+    # Setting Exclude here REPLACES RuboCop's default exclude list rather than
+    # extending it, so the paths it normally skips have to be restated. Without
+    # them RuboCop walks vendor/bundle and loads the .rubocop.yml shipped inside
+    # gems there, which pulls in plugins this project does not depend on.
+    - 'vendor/**/*'
+    - '.gem/**/*'
+    - 'node_modules/**/*'
+    - '.git/**/*'
     # Standalone cross-SDK test harness: carries its own Gemfile and is absent
     # from the gemspec's spec.files, so it is not held to the gem's style.
     - 'e2e-cli/**/*'