docs: updating flaking links (#20980)

(cherry picked from commit b36edc4)

Author: Borda

.github/CONTRIBUTING.md

@@ -3,7 +3,7 @@
 Welcome to the PyTorch Lightning community! We're building the most advanced research platform on the planet to implement the latest, best practices
 and integrations that the amazing PyTorch team and other research organization rolls out!
 
-If you are new to open source, check out [this blog to get started with your first Open Source contribution](https://devblog.pytorchlightning.ai/quick-contribution-guide-86d977171b3a).
+If you are new to open source, check out [this blog to get started with your first Open Source contribution](https://medium.com/pytorch-lightning/quick-contribution-guide-86d977171b3a).
 
 ## Main Core Value: One less thing to remember
 

src/pytorch_lightning/README.md

@@ -370,7 +370,7 @@ The PyTorch Lightning community is maintained by
 - [10+ core contributors](https://lightning.ai/docs/pytorch/stable/community/governance.html) who are all a mix of professional engineers, Research Scientists, and Ph.D. students from top AI labs.
 - 680+ active community contributors.
 
-Want to help us build Lightning and reduce boilerplate for thousands of researchers? [Learn how to make your first contribution here](https://devblog.pytorchlightning.ai/quick-contribution-guide-86d977171b3a)
+Want to help us build Lightning and reduce boilerplate for thousands of researchers? [Learn how to make your first contribution here](https://medium.com/pytorch-lightning/quick-contribution-guide-86d977171b3a)
 
 PyTorch Lightning is also part of the [PyTorch ecosystem](https://pytorch.org/ecosystem/) which requires projects to have solid testing, documentation and support.
 

tests/README.md

@@ -26,7 +26,7 @@ Additionally, for testing backward compatibility with older versions of PyTorch
 bash .actions/pull_legacy_checkpoints.sh
 ```
 
-Note: These checkpoints are generated to set baselines for maintaining backward compatibility with legacy versions of PyTorch Lightning. Details of checkpoints for back-compatibility can be found [here](https://github.com/Lightning-AI/pytorch-lightning/blob/master/tests/legacy/README.md).
+Note: These checkpoints are generated to set baselines for maintaining backward compatibility with legacy versions of PyTorch Lightning. Details of checkpoints for back-compatibility can be found [here](https://github.com/Lightning-AI/pytorch-lightning/tree/master/tests/legacy/README.md).
 
 You can run the full test suite in your terminal via this make script: