Reflect @Async executor qual. 3.2=>3.1.2 backport

@Async executor qualification has been backported to 3.1.2. This commit
updates all @since tags appropriately, as well as carrying over the
changes backported to the spring-task-3.1 schema.

Issue: SPR-6847, SPR-9443

spring-context/src/test/java/org/springframework/scheduling/annotation/AnnotationAsyncExecutionInterceptorTests.java

@@ -28,7 +28,7 @@ import static org.junit.Assert.*;
  * Unit tests for {@link AnnotationAsyncExecutionInterceptor}.
  *
  * @author Chris Beams
- * @since 3.2
+ * @since 3.1.2
  */
 public class AnnotationAsyncExecutionInterceptorTests {