group: Infrastructure documentation updates

Please be sure to double-check the file for any other version mentions as vale can miss.

Once a merge request is created link it to this issue. Note - only 1 merge request per issue to reduce the overhead as the technical writing team needs to review all changes.

Affected files:

 gitlab/doc/development/feature_categorization/index.md
 9:80  suggestion  If possible, remove the reference to 'GitLab 13.'.  gitlab.OutdatedVersions 

✔ 0 errors, 0 warnings and 1 suggestion in 1 file.