docs(comparison): correct GitLab CE multiple assignees for issues

[max-wittig]

GitLab CE doesn't support multiple assignees for issues.
That's an enterprise feature. See: https://docs.gitlab.com/ee/user/project/issues/multiple_assignees_for_issues.html

[codecov-io]

Codecov Report

Merging #4885 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #4885   +/-   ##
=======================================
  Coverage   37.22%   37.22%           
=======================================
  Files         305      305           
  Lines       45043    45043           
=======================================
  Hits        16766    16766           
+ Misses      25841    25840    -1     
- Partials     2436     2437    +1

Impacted Files	Coverage Δ
models/repo_indexer.go	50.84% <0%> (-1.28%)	⬇️
modules/process/manager.go	81.15% <0%> (+4.34%)	⬆️

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