CI: macOS py36_macos build fails
#### 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