Merge pull request #15149 from haberman/fix-21x-ruby

Fixed Ruby tests to pin Bundler to a version compatible with Ruby 2.7.

kokoro/linux/aarch64/ruby_build_and_run_tests_with_qemu_aarch64.sh

@@ -5,7 +5,7 @@ set -ex
 # go to the repo root
 cd $(dirname $0)/../../..
 
-gem install bundler
+gem install bundler -v 2.4.22
 
 cd ruby
 

kokoro/release/ruby/macos/ruby/ruby_build_environment.sh

@@ -29,7 +29,7 @@ gem install bundler --no-document
 time rvm install 2.7.0
 rvm use 2.7.0 --default
 gem install rake-compiler --no-document
-gem install bundler --no-document
+gem install bundler -v 2.4.22 --no-document
 rvm osx-ssl-certs status all
 rvm osx-ssl-certs update all
 set -ex