tests: Failure on macOS when sourceforge.net is unavailable

[moreati]

tar: Error opening archive: Unrecognized archive format
Traceback (most recent call last):
  File "/Users/runner/work/mitogen/mitogen/.ci/localhost_ansible_tests.py", line 23, in <module>
    subprocess.check_call(
    ~~~~~~~~~~~~~~~~~~~~~^
            "curl -O -L  https://sourceforge.net/projects/sshpass/files/sshpass/1.05/sshpass-1.05.tar.gz && \
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    ...<4 lines>...
            shell=True,
            ^^^^^^^^^^^
    )
    ^
  File "/Library/Frameworks/Python.framework/Versions/3.13/lib/python3.13/subprocess.py", line 419, in check_call
    raise CalledProcessError(retcode, cmd)
subprocess.CalledProcessError: Command 'curl -O -L  https://sourceforge.net/projects/sshpass/files/sshpass/1.05/sshpass-1.05.tar.gz &&                 tar xvf sshpass-1.05.tar.gz &&                 cd sshpass-1.05 &&                 ./configure &&                 sudo make install' returned non-zero exit status 1.
py313-mode_localhost-ansible11: exit 1 (16.86 seconds) /Users/runner/work/mitogen/mitogen> .ci/localhost_ansible_tests.py pid=5156
  py313-mode_localhost-ansible11: FAIL code 1 (85.37=setup[68.50]+cmd[16.86] seconds)
  evaluation failed :( (85.48 seconds)
Error: Process completed with exit code 1.

refs #1058