Fixing warnings in CLI startup

[ntouran]

This fixes warnings when you run armi on the CLI (as run from Python 3.12):

(armi) :~/code/armi$ armi
/home/nick/code/armi/armi/settings/settingsValidation.py:781: SyntaxWarning: invalid escape sequence '\d'
  fullV = "\d+\.\d+\.\d+"
/home/nick/code/armi/armi/settings/settingsValidation.py:782: SyntaxWarning: invalid escape sequence '\d'
  medV = "\d+\.\d+"
/home/nick/code/armi/armi/settings/settingsValidation.py:783: SyntaxWarning: invalid escape sequence '\d'
  minV = "\d+"

What is the change?

Add proper backslashes to regular expression. \d is an invalid escape sequence (where \n is a newline, \d means nothing).

Why is the change being made?

Because the code prints out 3 warnings on console as a first impression, and also:

Changed in version 3.12: Unrecognized escape sequences produce a SyntaxWarning. In a future Python version they will be eventually a SyntaxError.

src: https://docs.python.org/3/reference/lexical_analysis.html#escape-sequences

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Checklist

• This PR has only one purpose or idea.
• Tests have been added/updated to verify any new/changed code.

• The code style follows good practices.
• The commit message(s) follow good practices.

• The release notes have been updated if necessary.
• The documentation is still up-to-date in the doc folder.
• The dependencies are still up-to-date in pyproject.toml.