Upgrade detached plugins to versions with Guava compatibility fixes

[basil]

To be compatible with recent versions of Guava, Pipeline: API needs jenkinsci/workflow-api-plugin#135 and SCM API needs jenkinsci/scm-api-plugin#85. The former was released in 2.42, and the latter was released in 2.6.5. In preparation for the Guava upgrade in core, this PR bumps the versions of these detached plugins to those mentioned above. Since workflow-api 2.42 depends on workflow-step-api 2.23, we update that as well. Since scm-api 2.6.5 depends on structs 1.23, we update that as well.

Proposed changelog entries

• Update bundled versions of Pipeline: API, Pipeline: Step API, SCM API, and Structs plugins.

Proposed upgrade guidelines

N/A

Submitter checklist

• (If applicable) Jira issue is well described
• Changelog entries and upgrade guidelines are appropriate for the audience affected by the change (users or developer, depending on the change). Examples
  • Fill-in the Proposed changelog entries section only if there are breaking changes or other changes which may require extra steps from users during the upgrade
• Appropriate autotests or explanation to why this change has no tests
• For dependency updates: links to external changelogs and, if possible, full diffs

Desired reviewers

@MarkEWaite and @dheerajodha include links to Pipeline: API, Pipeline: Step API, SCM API, and Structs plugins in the references section of the changelog

Maintainer checklist

Before the changes are marked as ready-for-merge:

• There are at least 2 approvals for the pull request and no outstanding requests for change
• Conversations in the pull request are over OR it is explicit that a reviewer does not block the change
• Changelog entries in the PR title and/or Proposed changelog entries are correct
• Proper changelog labels are set so that the changelog can be generated automatically
• If the change needs additional upgrade steps from users, upgrade-guide-needed label is set and there is a Proposed upgrade guidelines section in the PR title. (example)
• If it would make sense to backport the change to LTS, a Jira issue must exist, be a Bug or Improvement, and be labeled as lts-candidate to be considered (see query).

[timja]

This PR is now ready for merge, after ~24 hours, we will merge it if there's no negative feedback.

Thanks!

[oleg-nenashev]

@basil would it help to have a Global project for Guava updates?

[basil]

@basil would it help to have a Global project for Guava updates?

I generally prefer to use Jira rather than GitHub issues or projects, and I have been using Jira successfully for this project up until now, so I don't see a pressing need for a global project. That having been said, I don't feel strongly about it, and if someone wants to create a global project to group Guava-related PRs together that is fine by me.