fix: use is None instead of == None (PEP 8 E711)

[harshadkhetpal]

Summary

Fix PEP 8 E711 violation in sagemaker-core/src/sagemaker/core/tools/templates.py.

Change:

# Before
elif value == None or not value:

# After
elif value is None or not value:

Comparison to None should always use is or is not, never the equality operators (==/!=). This is because None is a singleton and identity comparison is both semantically correct and slightly more efficient.

Testing

No behavior change — this is a style/correctness fix. Existing tests continue to pass.