fix(python): pin urllib3 version to <2.6 #SCD-642

[jablan]

https://github.com/urllib3/urllib3/blob/main/CHANGES.rst#260-2025-12-05 introduces a breaking change which causes errors with the client (presumably getheaders removal). Pinning the version to 2.5 until we adapt the library.

[Copilot]

Pull request overview

This PR pins the urllib3 dependency to versions below 2.6 to address compatibility issues. The change ensures that all Python OpenAPI generator templates consistently specify an upper bound for the urllib3 version requirement.

• Adds an upper bound constraint (<2.6) to urllib3 dependency specifications
• Updates both standard and experimental Python templates
• Ensures consistency across setup files, requirements files, and documentation

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
openapi-generator/templates/python/setup.mustache	Adds upper bound to urllib3 version in REQUIRES list
openapi-generator/templates/python/requirements.mustache	Adds upper bound to urllib3 version in requirements
openapi-generator/templates/python/python-experimental/setup.mustache	Adds upper bound to urllib3 version in experimental setup
openapi-generator/templates/python/python-experimental/requirements.mustache	Adds upper bound to urllib3 version in experimental requirements
openapi-generator/templates/python/python-experimental/README_onlypackage.mustache	Updates documentation to reflect urllib3 version constraint
openapi-generator/templates/python/README_onlypackage.mustache	Updates documentation to reflect urllib3 version constraint

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