Dockerfile: copy vendor directory to run bundle install

In case some of the gems are in `vendor/gems`.

Author: noma4i

railties/lib/rails/generators/rails/app/templates/Dockerfile.tt

@@ -52,7 +52,8 @@ RUN curl -fsSL https://bun.sh/install | bash -s -- "bun-v${BUN_VERSION}"
 
 <% end -%>
 # Install application gems
-COPY Gemfile Gemfile.lock ./
+COPY Gemfile Gemfile.lock vendor ./
+
 RUN bundle install && \
     rm -rf ~/.bundle/ "${BUNDLE_PATH}"/ruby/*/cache "${BUNDLE_PATH}"/ruby/*/bundler/gems/*/.git<% if depend_on_bootsnap? -%> && \
     bundle exec bootsnap precompile --gemfile<% end %>
@@ -116,4 +117,4 @@ CMD ["./bin/rails", "server"]
 # Start server via Thruster by default, this can be overwritten at runtime
 EXPOSE 80
 CMD ["./bin/thrust", "./bin/rails", "server"]
-<% end -%>
+<% end -%>