Integration tests for list data type occasionally fail

[estolfo]

Build scan:

Repro line:
https://github.com/logstash-plugins/logstash-input-redis/blob/main/spec/inputs/redis_spec.rb#L35-L68

Reproduces locally?:
no

Applicable branches:
main

Failure history:

https://app.travis-ci.com/github/logstash-plugins/logstash-input-redis/jobs/636386167
https://app.travis-ci.com/github/logstash-plugins/logstash-input-redis/jobs/636785304

Failure excerpt:

w Enable Watchlogstash-1  | inputs/redis
w Enable Watchlogstash-1  |   should read events from a list
w Enable Watchlogstash-1  |   should read events from a list using batch_count (default 125) (FAILED - 1)
w Enable Watchlogstash-1  | 
w Enable Watchlogstash-1  | Failures:
w Enable Watchlogstash-1  | 
w Enable Watchlogstash-1  |   1) inputs/redis should read events from a list using batch_count (default 125)
w Enable Watchlogstash-1  |      Failure/Error: expect(events[1000].get('sequence')).to eq(1000)
w Enable Watchlogstash-1  |      
w Enable Watchlogstash-1  |      NoMethodError:
w Enable Watchlogstash-1  |        undefined method `get' for nil:NilClass
w Enable Watchlogstash-1  |        Did you mean?  getc
w Enable Watchlogstash-1  |                       gets
w Enable Watchlogstash-1  |                       gem
w Enable Watchlogstash-1  |      # ./spec/inputs/redis_spec.rb:28:in `process'
w Enable Watchlogstash-1  |      # ./spec/inputs/redis_spec.rb:67:in `block in <main>'