Fix Python logging.warn() deprecation warnings

[makubacki]

Description

Updates logging.warn() to logging.warning() to prevent
deprecation warnings like this:

.pytool\Plugin\UncrustifyCheck\UncrustifyCheck.py:386:
DeprecationWarning: The 'warn' function is deprecated, use
'warning' instead

• Impacts functionality?
  • Functionality - Does the change ultimately impact how firmware functions?
  • Examples: Add a new library, publish a new PPI, update an algorithm, ...
• Impacts security?
  • Security - Does the change have a direct security impact on an application,
    flow, or firmware?
  • Examples: Crypto algorithm change, buffer overflow fix, parameter
    validation improvement, ...
• Breaking change?
  • Breaking change - Will anyone consuming this change experience a break
    in build or boot behavior?
  • Examples: Add a new library class, move a module to a different repo, call
    a function in a new library class in a pre-existing module, ...
• Includes tests?
  • Tests - Does the change include any explicit test code?
  • Examples: Unit tests, integration tests, robot tests, ...
• Includes documentation?
  • Documentation - Does the change contain explicit documentation additions
    outside direct code modifications (and comments)?
  • Examples: Update readme file, add feature readme file, link to documentation
    on an a separate Web page, ...

How This Was Tested

• Review Python code for log.warn() usage
• Check logs that reported issue earlier after changee

Integration Instructions

N/A