Update python fastapi urllib3 to newer version

[wing328]

to close #22633

PR checklist

• Read the contribution guidelines.
• Pull Request title clearly describes the work in the pull request and Pull Request description provides details about how to validate the work. Missing information here may result in delayed response from the community.
• Run the following to build the project and update samples:

  ./mvnw clean package || exit
  ./bin/generate-samples.sh ./bin/configs/*.yaml || exit
  ./bin/utils/export_docs_generators.sh || exit
  

  (For Windows users, please run the script in WSL)
  Commit all changed files.
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• File the PR against the correct branch: master (upcoming 7.x.0 minor release - breaking changes with fallbacks), 8.0.x (breaking changes without fallbacks)
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Summary by cubic

Updated the Python FastAPI generator and sample to use urllib3 2.6.3 instead of 2.6.0. This pulls in upstream fixes and keeps dependencies current.

• Dependencies
  • Bumped urllib3 from 2.6.0 to 2.6.3 in requirements.mustache and sample requirements.txt.

^{Written for commit fc5dd1b. Summary will update on new commits.}

[cubic-dev-ai]

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