chore: mark as experimental

Author: marco-ippolito

doc/api/cli.md

@@ -1461,6 +1461,8 @@ added:
   - REPLACEME
 -->
 
+> Stability: 1 - Experimental
+
 Instructs the test runner to bail out if a test failure occurs.
 See the documentation on [test bailout][] for more details.
 

doc/api/test.md

@@ -609,6 +609,8 @@ added:
   - REPLACEME
 -->
 
+> Stability: 1 - Experimental
+
 The `--test-bail` flag provides a way to stop the test execution
 as soon as a test fails.
 By enabling this flag, the test runner will exit the test suite early