host-select: fix compatibility with force-condemned hosts

[oliver-sanders]

Supersedes #6623

Fix an issue with host-select which prevented us from condemning hosts in "force mode".

Also, better link into the "auto restart" docs which can be found here: https://cylc.github.io/cylc-doc/stable/html/plugins/main-loop/built-in/cylc.flow.main_loop.auto_restart.html#module-cylc.flow.main_loop.auto_restart

I am not going to go applying terminology changes to this long-standing feature as part of this bugfix (out of scope).

Check List

• I have read CONTRIBUTING.md and added my name as a Code Contributor.
• Contains logically grouped changes (else tidy your branch by rebase).
• Does not contain off-topic changes (use other PRs for other changes).
• Applied any dependency changes to both setup.cfg (and conda-environment.yml if present).
• Tests are included (or explain why tests are not needed).
• Changelog entry included if this is a change that can affect users
• Cylc-Doc pull request opened if required at cylc/cylc-doc/pull/XXXX.
• If this is a bug fix, PR should be raised against the relevant ?.?.x branch.

[oliver-sanders]

Note, this line is covered by the test amended in this PR (confirm by running it on master), however, that test is not run in CI due to it's shared filesystem setup.