Pin setuptools in GPU tests

[lantiga]

What does this PR do?

This PR makes CI green by:

• pinning setuptools in GPU tests, similar to Pin setuptools in release container #20488
• fixing doc references

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📚 Documentation preview 📚: https://pytorch-lightning--20489.org.readthedocs.build/en/20489/

[github-actions]

⚡ Required checks status: All passing 🟢

Groups summary

🟢 pytorch_lightning: Azure GPU

Check ID	Status
pytorch-lightning (GPUs) (testing Lightning | latest)	success	✅
pytorch-lightning (GPUs) (testing PyTorch | latest)	success	✅

These checks are required after the changes to .azure/gpu-tests-pytorch.yml.

🟢 pytorch_lightning: Benchmarks

Check ID	Status
lightning.Benchmarks	success	✅

These checks are required after the changes to .azure/gpu-benchmarks.yml.

🟢 pytorch_lightning: Docs

Check ID	Status
docs-make (pytorch, doctest)	success	✅
docs-make (pytorch, html)	success	✅

These checks are required after the changes to docs/source-pytorch/common/index.rst.

🟢 lightning_fabric: Azure GPU

Check ID	Status
lightning-fabric (GPUs) (testing Fabric | latest)	success	✅
lightning-fabric (GPUs) (testing Lightning | latest)	success	✅

These checks are required after the changes to .azure/gpu-tests-fabric.yml.

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Thank you for your contribution! 💜

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[Borda]

Btw, why there are so many PRs with pinning setuptools?