🔧 Update TestDriven link to course in sponsors (#2435)

docs/en/data/sponsors.yml

@@ -3,7 +3,7 @@ gold:
     title: The launchpad for all your (team's) ideas
     img: https://fastapi.tiangolo.com/img/sponsors/deta.svg
 silver:
-  - url: https://testdriven.io/
+  - url: https://testdriven.io/courses/tdd-fastapi/
     title: Learn to build high-quality web apps with best practices
     img: https://fastapi.tiangolo.com/img/sponsors/testdriven.svg
   - url: https://jobs.bywetransfer.com/