CI: macOS py36_macos build fails

[AlexKirko]

Problem description

Currently macOS py36_macos Azure pipeline fails with this build error:

    ImportError: dlopen(/Users/runner/miniconda3/lib/python3.7/lib-dynload/_ctypes.cpython-37m-darwin.so, 2): Library not loaded: @rpath/libffi.6.dylib
      Referenced from: /Users/runner/miniconda3/lib/python3.7/lib-dynload/_ctypes.cpython-37m-darwin.so
      Reason: image not found

Seen on #31563 and #31977

[MarcoGorelli]

Seems to be working now, at least on #31795

[AlexKirko]

Seems to have recovered. Closing.