[3.12] gh-118310: Fix documentation for enum.Enum.__new__ (GH-118311)

[miss-islington]

The provided example was incorrect:

• The example enum was missing the int mixin as implied by the context
• The value of int('1a', 16) was incorrectly given as 17
  (should be 26)
  (cherry picked from commit 48e52fe)

Co-authored-by: Momo Eissenhauer [email protected]

• Issue: Incorrect example in docs for enum.Enum.__new__ #118310

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📚 Documentation preview 📚: https://cpython-previews--118699.org.readthedocs.build/