Don't sync spec folder from Rails' vendored gems

Excluding these files should save ~1.7MiB:

root@16.8.1-ee:/opt/gitlab/embedded/service/gitlab-rails# du -shc
gems/*.yml gems/config gems/README.md gems/*/spec vendor/gems/*/spec
vendor/gems/README.md
4.0K    gems/gem-pg.gitlab-ci.yml
4.0K    gems/gem.gitlab-ci.yml
8.0K    gems/config
4.0K    gems/README.md
84K     gems/activerecord-gitlab/spec
52K     gems/click_house-client/spec
28K     gems/csv_builder/spec
32K     gems/gitlab-backup-cli/spec
8.0K    gems/gitlab-database-load_balancing/spec
20K     gems/gitlab-database-lock_retries/spec
52K     gems/gitlab-housekeeper/spec
120K    gems/gitlab-http/spec
20K     gems/gitlab-rspec/spec
52K     gems/gitlab-rspec_flaky/spec
28K     gems/gitlab-safe_request_store/spec
200K    gems/gitlab-schema-validation/spec
32K     gems/gitlab-secret_detection/spec
76K     gems/gitlab-utils/spec
432K    gems/ipynbdiff/spec
152K    vendor/gems/cloud_profiler_agent/spec
40K     vendor/gems/devise-pbkdf2-encryptable/spec
28K     vendor/gems/mail-smtp_pool/spec
52K     vendor/gems/microsoft_graph_mailer/spec
28K     vendor/gems/omniauth-azure-oauth2/spec
20K     vendor/gems/omniauth-gitlab/spec
24K     vendor/gems/omniauth-salesforce/spec
48K     vendor/gems/omniauth_crowd/spec
36K     vendor/gems/sidekiq-reliable-fetch/spec
4.0K    vendor/gems/README.md
1.7M    total

Author: splattael

config/software/gitlab-rails.rb

@@ -234,14 +234,20 @@
   sync './', "#{install_dir}/embedded/service/gitlab-rails/", exclude: %w(
     .git
     .gitignore
-    spec
+    app/assets
+    ee/app/assets
     ee/spec
     features
+    gems/*.yml
+    gems/*/spec
+    gems/config
+    gems/README.md
     qa
     rubocop
-    app/assets
+    spec
     vendor/assets
-    ee/app/assets
+    vendor/gems/*/spec
+    vendor/gems/README.md
     workhorse
   )