Fix previous_minor method of ReleaseToos::Version

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Describe in detail what your merge request does and why.

Content

Fix previous_minor method of ReleaseToos::Version

• Return a minor version string, instead of full string with the patch number, e.g. 17.10 instead of 17.10.0
• In case of a major version (e.g. 18.0), use GitlabReleasesGemClient.previous_minors to determine. This logic is more reliable than the version server, which may have the version order wrong.

Regrading the removal of ".0" at the end of the version string, I checked and found previous_minor used only with the Version class, which handles it well:

[1] pry(main)> ReleaseTools::Version.new('17.10')
=> "17.10.0"
[3] pry(main)> ReleaseTools::Version.new('17.10').stable_branch(ee: true)
=> "17-10-stable-ee"

Testing

[3] pry(main)> ReleaseTools::GitlabReleasesGemClient.previous_minors('17.11')
=> ["17.11", "17.10", "17.9"]

[1] pry(main)> ReleaseTools::Version.new('18.0.0').previous_minor
=> "17.11"

Ref: gitlab-com/gl-infra/delivery#21073 (closed)