Fix Ruby 2.7 use of Hash#transform_keys in bulk update call

What does this MR do and why?

!111729 (merged) introduced the use of Hash#transform_keys with a Hash parameter (https://ruby-doc.org/core-3.1.0/Hash.html), which is only available in Ruby 3. To ensure backwards compatibility, use a more verbose implementation.

This fixes the Ruby 2.7 job failure in https://gitlab.com/gitlab-org/gitlab/-/jobs/3797297862.

How to set up and validate locally

1. Apply this diff:

diff --git a/.tool-versions b/.tool-versions
index ecddbdfeadce..0442b347209d 100644
--- a/.tool-versions
+++ b/.tool-versions
@@ -2,6 +2,6 @@ minio 2022-07-15T03-44-22Z
 nodejs 16.15.0
 postgres 12.13 13.9
 redis 6.2.7
-ruby 3.0.5
+ruby 2.7.7
 rust 1.65.0
 yarn 1.22.19
diff --git a/spec/support/helpers/gitaly_setup.rb b/spec/support/helpers/gitaly_setup.rb
index 398a2a20f2fa..e7e920a1220e 100644
--- a/spec/support/helpers/gitaly_setup.rb
+++ b/spec/support/helpers/gitaly_setup.rb
@@ -199,7 +199,10 @@ def check_gitaly_config!
 
     LOGGER.debug "Checking gitaly-ruby bundle...\n"
     out = ENV['CI'] ? $stdout : '/dev/null'
-    abort 'bundle check failed' unless system(env, 'bundle', 'check', out: out, chdir: gemfile_dir)
+
+    unless system(env, 'bundle', 'check', out: out, chdir: gemfile_dir)
+      system(env, 'bundle', 'install', out: out, chdir: gemfile_dir)
+    end
   end
 
   def connect_proc(toml)

2. Run bundle exec rspec ./spec/requests/api/graphql/mutations/issues/bulk_update_spec.rb.

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