Remove bundle lock --add-platform step

The Gemfile.lock already has x86_64-linux platform. Removing this step
to prevent lockfile modifications during CI.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: justin808

.github/workflows/ruby.yml

@@ -47,7 +47,7 @@ jobs:
           path: vendor/bundle
           key: root-gem-cache-${{ matrix.ruby }}-${{ hashFiles('Gemfile.lock') }}
       - name: Install Ruby Gems
-        run: bundle lock --add-platform 'x86_64-linux' && bundle check --path=vendor/bundle || bundle _2.4.9_ install --path=vendor/bundle --jobs=4 --retry=3
+        run: bundle check --path=vendor/bundle || bundle _2.4.9_ install --path=vendor/bundle --jobs=4 --retry=3
       - run: yarn
       - run: bundle exec rake react:update
       - run: bundle exec rake ujs:update