Update CI documentation reference in README

Replace obsolete Concourse pipeline reference with GitHub Actions.
The Concourse link returns 404.

See gh-35746
Signed-off-by: Moad ELFATIHI <elfatihi.moad@gmail.com>

README.md

@@ -27,7 +27,7 @@ See the [Build from Source](https://github.com/spring-projects/spring-framework/
 
 ## Continuous Integration Builds
 
-Information regarding CI builds can be found in the [Spring Framework Concourse pipeline](ci/README.adoc) documentation.
+Information regarding CI builds can be found in the [GitHub Actions workflows](.github/workflows).
 
 ## Stay in Touch