Fix Python enum members generating tuple values

[AayushP123]

Summary

Removes trailing commas from generated Python string enum assignments. Adds enum writer coverage for regular and escaped wire values.

A trailing comma makes a Python expression such as "red", a one-element tuple, preventing incoming string values from matching generated enum members during deserialization.

Validation

dotnet test tests/Kiota.Builder.Tests/Kiota.Builder.Tests.csproj --no-restore --nologo --filter 'FullyQualifiedName~Writers.Python.CodeEnumWriterTests' (11 passed)

Fixes #7811

[Copilot]

Pull request overview

This PR fixes Python enum generation so that enum members are emitted as plain string values (instead of single-element tuples), aligning the generated output with class MyEnum(str, Enum) semantics.

Changes:

• Update the Python CodeEnumWriter to emit enum members without a trailing comma, ensuring values are strings.
• Strengthen Python enum writer tests to assert the absence of the trailing comma and validate correct line termination.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/Kiota.Builder/Writers/Python/CodeEnumWriter.cs	Removes the trailing comma so generated Python enum members are string literals, not tuples.
tests/Kiota.Builder.Tests/Writers/Python/CodeEnumWriterTests.cs	Updates assertions to verify the new string-member emission and explicitly reject the old tuple syntax.