Specify last compatible CLI version for server 4.2 [ONPREM-237]

[christian-stephen]

Description

A brief description of the changes.

The CLI is being updated to use the runner API v3 (https://github.com/CircleCI-Public/circleci-cli/pull/1065), which is only supported on 4.3+. While 4.2 is now unsupported with the release of 4.6, this is just a courtesy for users still on 4.2.

Reasons

A link to a GitHub and/or JIRA issue (if applicable). Otherwise, a brief sentence about why you made these changes.

https://circleci.atlassian.net/browse/ONPREM-237

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