Fix variable passing in redis-hll migration spec

What does this MR do and why?

This MR is a repeat of !140553 (merged) as the migration is being performed again with the similar specs.

This MR fixes how value is passed in to the set_redis_hll method in spec/migrations/20240116072014_change_i_code_review_create_mr_keys_from_hll_to_integer_spec.rb.rb. Currently, value: 7 would mean we pass {value: 7} to Gitlab::Redis::HLL.add(...). What the Redis server receives is PFADD <key> "{:value=>7}" instead of PFADD <key> 7.

Hashes are silently acceptable in redis v4.8.0 gem as .to_s is called on anything that is not an Array: https://github.com/redis/redis-rb/blob/v4.8.0/lib/redis/connection/command_helper.rb#L20

However, this will raise an error in in redis v5.x gem as seen in the failed job. See an example of a failed job in https://gitlab.com/gitlab-org/gitlab/-/jobs/5945638640

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