[23.1] FileInput no longer accept 'U' in the file mode

[bgruening]

From the 3.11 release notes:

FileInput no longer accept 'U' (“universal newline”) in the file mode. In Python 3, “universal newline” mode is used by default whenever a file is opened in text mode, and the 'U' flag has been deprecated since Python 3.3.

See also https://docs.python.org/3.5/library/functions.html#open

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