Update Distributed Systems edition from 3rd to 4th (#13043)

Author: double-tilde

books/free-programming-books-subjects.md

@@ -200,7 +200,7 @@ Books that cover a specific programming language can be found in the [BY PROGRAM
 * [Cloud Computing for Science and Engineering](https://cloud4scieng.org/chapters/) - Ian Foster, Dennis B. Gannon *( :construction: in process)*
 * [Cloud Design Patterns](https://docs.microsoft.com/en-us/azure/architecture/patterns/)
 * [Designing Distributed Systems](https://azure.microsoft.com/en-us/resources/designing-distributed-systems/) *(account required)*
-* [Distributed Systems 3rd edition](https://www.distributed-systems.net/index.php/books/ds3/) - Maarten van Steen, Andrew S. Tanenbaum *(email address required)*
+* [Distributed Systems 4th edition](https://www.distributed-systems.net/index.php/books/ds4/ds4-ebook/) - Maarten van Steen, Andrew S. Tanenbaum *(email address required)*
 * [How to optimize storage costs using Amazon S3](https://aws.amazon.com/s3/cloud-storage-cost-optimization-ebook/) - AWS (PDF)
 * [Kubernetes Hardening Guidance](https://media.defense.gov/2022/Aug/29/2003066362/-1/-1/0/CTR_KUBERNETES_HARDENING_GUIDANCE_1.2_20220829.PDF) - NSA, CISA (PDF)
 * [Learn Azure in a Month of Lunches](https://clouddamcdnprodep.azureedge.net/gdc/2014519/original) - Iain Foulds (PDF)