Add Python 3.14 and 3.14t to the testing

[cclauss]

https://www.python.org/downloads/release/python-3140/

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pip install -U can be quite opaque to readers because pip install currently has six --u* options, including --user.

pip install --upgrade makes the intention clearer in code that others will read.

% python3 -m pip install --help | grep "\-\-u"

  --user                      Install to the Python user install directory for
  -U, --upgrade               Upgrade all specified packages to the newest
  --upgrade-strategy <upgrade_strategy>
  --use-pep517                Use PEP 517 for building source distributions
  --use-feature <feature>     Enable new functionality, that may be backward
  --use-deprecated <feature>  Enable deprecated functionality, that will be

@cunla