Backport of executor: fail early on reattach if listener is not executor into release/1.9.x

[hc-github-team-nomad-core]

Backport

This PR is auto-generated from #24538 to be assessed for backporting due to the inclusion of the label backport/1.9.x.

The below text is copied from the body of the original PR.

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Description

Fixes a bug reported by Windows users where Nomad was killing random processes on reboot. This was due to the reattach config containing a PID and RPC address that was now occupied by other processes/listeners. When Nomad would attempt to make an RPC, it would fail, and kill the process. With this change, we fail early on reattach, and do not kill the process.

Testing & Reproduction steps

Reproduction involves simulating this scenario via overriding the reattach PID when starting a task to a known PID (another bash session), rebooting Nomad, killing the executor process, and listening on the reattach address.

Links

Fixes GH #23969

Contributor Checklist

• Changelog Entry If this PR changes user-facing behavior, please generate and add a
  changelog entry using the make cl command.
• Testing Please add tests to cover any new functionality or to demonstrate bug fixes and
  ensure regressions will be caught.
• Documentation If the change impacts user-facing functionality such as the CLI, API, UI,
  and job configuration, please update the Nomad website documentation to reflect this. Refer to
  the website README for docs guidelines. Please also consider whether the
  change requires notes within the upgrade guide.

Reviewer Checklist

• Backport Labels Please add the correct backport labels as described by the internal
  backporting document.
• Commit Type Ensure the correct merge method is selected which should be "squash and merge"
  in the majority of situations. The main exceptions are long-lived feature branches or merges where
  history should be preserved.
• Enterprise PRs If this is an enterprise only PR, please add any required changelog entry
  within the public repository.

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Overview of commits

• 4e2d967