Make browserslist known as a frontend file

If we are adjusting browser versions, we want a full pipeline to see the
effects (e.g. bundle size changes, etc.). Furthermore Danger should know
about the browserslist file.

.gitlab/ci/rules.gitlab-ci.yml

@@ -162,6 +162,7 @@
 
 .frontend-build-patterns: &frontend-build-patterns
   - "{package.json,yarn.lock}"
+  - ".browserslistrc"
   - "babel.config.js"
   - "config/webpack.config.js"
   - "config/**/*.js"
@@ -170,6 +171,7 @@
 
 .frontend-patterns: &frontend-patterns
   - "{package.json,yarn.lock}"
+  - ".browserslistrc"
   - "babel.config.js"
   - "jest.config.{base,integration,unit}.js"
   - ".csscomb.json"

tooling/danger/project_helper.rb

@@ -54,6 +54,7 @@ module Tooling
         %r{\A(ee/)?scripts/frontend/} => :frontend,
         %r{(\A|/)(
           \.babelrc |
+          \.browserslistrc |
           \.eslintignore |
           \.eslintrc(\.yml)? |
           \.nvmrc |