Fix migrate-from-v12.10.0 job not working with Ruby v2.7

The grpc and google-protobuf gems need to be updated to work with Ruby
v2.7. When we check out the v12.10.0-ee tag, we manually patch the
versions in the Gemfile before attempting to run the migration.

.gitlab/ci/rails.gitlab-ci.yml

@@ -285,6 +285,8 @@ db:migrate-from-v12.10.0:
     - '[[ -d "ee/" ]] || export TAG_TO_CHECKOUT="v12.10.0"'
     - git fetch https://gitlab.com/gitlab-org/$PROJECT_TO_CHECKOUT.git $TAG_TO_CHECKOUT
     - git checkout -f FETCH_HEAD
+    - sed -i -e "s/gem 'grpc', '~> 1.24.0'/gem 'grpc', '~> 1.30.2'/" Gemfile # Update gRPC for Ruby 2.7
+    - sed -i -e "s/gem 'google-protobuf', '~> 3.8.0'/gem 'google-protobuf', '~> 3.12.0'/" Gemfile
     - bundle update google-protobuf grpc bootsnap
     - bundle install $BUNDLE_INSTALL_FLAGS
     - date