Fix reinstall test failing on MacOS due to rsync change

[MetRonnie]

For some reason on GH Actions MacOS we have started seeing "recv" instead of "send" in rsync here:

REINSTALL cit-20250901T091622Z/test_reinstall/test_permissions_change/52f05762 from /private/var/folders/x7/ch5v91h56_zbvbd1y2f600dm0000gn/T/pytest-of-runner/pytest-1/popen-gw4/test_permissions_change0/src
.f...p... recv myscript

\x1b[38;5;248mTIP: You can "exclude" files/dirs to prevent Cylc from installing or overwriting
     them by adding them to the .cylcignore file. See cylc reinstall --help.\x1b[0m

\x1b[1mReinstall would make the above changes.\x1b[0m
\x1b[35mNo changes made: reinstall cancelled.\x1b[0m

Possibly macos-latest has changed to 15

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).
• No dependency changes or tests or changelog or docs needed
• If this is a bug fix, PR should be raised against the relevant ?.?.x branch.

[oliver-sanders]

The change is a tad concerning.

The change from send => recv suggests a change of perspective from server => client which is rather odd.

I don't think we do any remote stuff on the Mac OS tests, so I guess the server and client are the same host. Maybe that's it?

[MetRonnie]

My guess is macos-latest has changed to 15 this week and on the new runner rsync is behaving in "pull" mode even though it is still local: https://github.com/cylc/cylc-flow/actions/runs/17375118712/job/49319610412#step:8:1178

rsync -a --checksum --out-format=%o %n%L --no-t --delete --exclude=/_cylc-install --exclude=/rose-suite.conf /private/var/folders/x7/ch5v91h56_zbvbd1y2f600dm0000gn/T/pytest-of-runner/pytest-1/popen-gw1/test_permissions_change0/src/ /Users/runner/cylc-run/cit-20250901T103938Z/test_reinstall/test_permissions_change/a4afc7cb/ --out-format=%i %o %n%L

The tests still pass as the files are being copied correctly

Edit: tested

$ rsync -an --out-format='%i %o %n%L' localhost:/path/to/file /path/to/elsewhere

and get the same recv output instead of send if you remove localhost:

[hjoliver]

The explanation seems vaguely plausible.