windows-ci: temporarily allow Windows jobs to fail

We have unfortunately ran out of free credit on the runners we were using from
OVH for the Windows CI. We will be disabling the two remaining ones on the 30th
of September, hence we need the CI to pass even if Windows jobs cannot start as
a temporary measure. Hopefully we can find another way of getting Windows
runners soon.

Differential Revision: https://phab.mercurial-scm.org/D11499

contrib/heptapod-ci.yml

@@ -152,6 +152,7 b' check-pytype-py3:'
 # that satisfies the various shebang lines and delegates to `py -3`.
 .window_runtests_template: &windows_runtests
     <<: *all
+    when: manual  # we don't have any Windows runners anymore at the moment
     stage: tests
     before_script:
       - C:/MinGW/msys/1.0/bin/sh.exe --login -c 'cd "$OLDPWD" && ls -1 tests/test-check-*.* > C:/Temp/check-tests.txt'