ci: switch to codecov cli on appveyor

This change replaces the legacy codecov uploader on macos with a
specific codecov-cli (the uploader's modern replacement) version that is known
to support several CPUs.
This does not solve the issue that coverage reports are not uploaded to
codecov, but it fixes the issue that the CPU mismatch caused a non-zero
exit code that would lead to a CI failure even when all tests passed.
Fixes datalad#756

.appveyor.yml

@@ -118,7 +118,7 @@ environment:
       PY: 3.8
       INSTALL_GITANNEX: git-annex
       DATALAD_LOCATIONS_SOCKETS: /Users/appveyor/DLTMP/sockets
-      CODECOV_BINARY: https://uploader.codecov.io/latest/macos/codecov
+      CODECOV_BINARY: https://cli.codecov.io/v0.7.4/macos/codecov
       DATALAD_TESTS_SSH: 1
       # no docker on Mac, we log into self
       # 'test_publish_target_url' relies git-annex being installed on the
@@ -333,7 +333,8 @@ for:
       - python -m coverage xml
       - "curl -Os $CODECOV_BINARY"
       - chmod +x codecov
-      - ./codecov
+      # the do-upload subcommand seems to work for the codecov-cli and legacy uploader
+      - ./codecov do-upload
 
     on_finish:
       # conditionally block the exit of a CI run for direct debugging