CI: Fixing error in code checks in GitHub actions
xref https://github.com/pandas-dev/pandas/pull/29546#issuecomment-554807243

Looks like the code in one of the checks in `ci/code_checks.sh` uses another encoding for spaces and other characters. I guess it was generated from Windows, Azure-pipelines is not sensitive to the different encoding, but GitHub actions is.

Probably worth doing some more research and adding a check that makes sure this new encoding is not introduced anymore.

CC: @gfyoung @jreback 