Update Ruby gems to support Ruby 3.0

The following gems currently have the Ruby version restrictions that prevent us from using Ruby 3.0:

• gitlab-fog-google - this gem requires this MR to be merged first: gitlab-fog-google!5 (merged)
• unicorn - 5.7.0 is the minimum version that supports Ruby 3.0
• redis-namespace - 1.8.1 is the minimum version that supports Ruby 3.0
• js_regex - probably should be updated as well, the reason must be verified
• simplecov - should be updated to update the version of simplecov-ruby gem
• grpc - contains a dependency that should be updated to support Ruby 3.0
• unleash - 3.2.2 is the minimum version that supports Ruby 3.0
• json_schemer - 0.2.12 is the minimum version that supports Ruby 3.0
• listen - 3.5.1 is the minimum version that supports Ruby 3.0 (the version can be modified in Gemfile.lock directly)
• sanitize - 5.2.2 is the minimum version that supports Ruby 3.0 (See https://github.com/rgrove/sanitize/blob/main/HISTORY.md#522-2021-01-06)