chore(init-templates/python): correct virtual environment typo (#12230)

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This is a suggested fix for #12229, a small typo in the init templates for Python.

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

Author: idanlupinsky

packages/aws-cdk/lib/init-templates/v2/app/python/.template.gitignore

@@ -2,7 +2,7 @@
 package-lock.json
 __pycache__
 .pytest_cache
-.env
+.venv
 *.egg-info
 
 # CDK asset staging directory