Gitlab::Instrumentation::RedisInterceptor isn't Redis 4 compatible

Redis 3 support was deprecated in %13.0 but we should still be supporting Redis 4. Gitlab::Instrumentation::RedisInterceptor is currently incompatible, see this pipeline run for info.

Failures:
  1) Gitlab::Instrumentation::RedisInterceptor read and write setup: [[:xadd, "mystream", "123456-89", "foo", "bar"]], command: [:xrange, "mystream", "-", "+"], expect_write: 16, expect_read: 15 counts bytes read and written
     Failure/Error: super(*args, &block)
     Redis::CommandError:
       ERR unknown command `xadd`, with args beginning with: `mystream`, `123456-89`, `foo`, `bar`,
     # ./vendor/ruby/2.6.0/gems/redis-4.1.3/lib/redis/client.rb:126:in `call'
     # ./lib/gitlab/instrumentation/redis_interceptor.rb:15:in `call'
     # ./vendor/ruby/2.6.0/gems/redis-4.1.3/lib/redis.rb:88:in `block in call'
     # ./vendor/ruby/2.6.0/gems/redis-4.1.3/lib/redis.rb:52:in `block in synchronize'
     # /usr/local/lib/ruby/2.6.0/monitor.rb:235:in `mon_synchronize'
     # ./vendor/ruby/2.6.0/gems/redis-4.1.3/lib/redis.rb:52:in `synchronize'
     # ./vendor/ruby/2.6.0/gems/redis-4.1.3/lib/redis.rb:87:in `call'
     # ./spec/lib/gitlab/instrumentation/redis_interceptor_spec.rb:35:in `block (6 levels) in <top (required)>'
     # ./spec/lib/gitlab/instrumentation/redis_interceptor_spec.rb:35:in `each'
     # ./spec/lib/gitlab/instrumentation/redis_interceptor_spec.rb:35:in `block (5 levels) in <top (required)>'

Blocks !39709 (merged)