Update README

Author: marcprux

README.md

@@ -79,7 +79,7 @@ which may be a pre-release build.
 Snapshots can be specified with their full name, like `6.1-DEVELOPMENT-SNAPSHOT-2025-03-25-a`,
 or the most recent snapshot/nightly build can be specified with `nightly-6.1`. 
 
-> [!NOTE]
+> [!WARNING]
 > The Swift Testing framework is only available in the 6.1 SDK, so if your project
 > uses Swift Testing, you should either use the `nightly-6.1` version, or disable
 > testing by setting `build-tests: false`.