Allow OpenSSH@9

[giordano]

Since there are conflicts in #74, to more quickly move forward I opened a new PR.

Fix #73, close #74.

[giordano]

All tests pass locally for me on both aarch64-darwin and x86_64-w64-mingw32 (the latter was tested using https://github.com/mxschmitt/action-tmate):

Test Summary:   | Pass  Total   Time
DocumenterTools |   35     35  16.0s
     Testing DocumenterTools tests passed

[giordano]

Also, you may want to change the settings of this repository to only "Require approval for first-time contributors who are new to GitHub" in the "Fork pull request workflows from outside collaborators" section, otherwise you'll always need to click on manually approve running CI.