Spring Fix test compilation warnings

The following warnings can be seen during the compilation of the tests:

> Task :spring-beans:compileTestFixturesJava
/home/seb/workspace/spring-framework/spring-core/build/classes/java/main/org/springframework/lang/Nullable.class: warning: Cannot find annotation method 'when()' in type 'Nonnull': class file for javax.annotation.Nonnull not found
warning: unknown enum constant When.MAYBE
  reason: class file for javax.annotation.meta.When not found
/home/seb/workspace/spring-framework/spring-core/build/classes/java/main/org/springframework/lang/NonNullApi.class: warning: Cannot find annotation method 'value()' in type 'TypeQualifierDefault': class file for javax.annotation.meta.TypeQualifierDefault not found
/home/seb/workspace/spring-framework/spring-core/build/classes/java/main/org/springframework/lang/NonNullFields.class: warning: Cannot find annotation method 'value()' in type 'TypeQualifierDefault'
4 warnings

> Task :spring-aop:compileTestFixturesJava
/home/seb/workspace/spring-framework/spring-core/build/classes/java/main/org/springframework/lang/Nullable.class: warning: Cannot find annotation method 'when()' in type 'Nonnull': class file for javax.annotation.Nonnull not found
warning: unknown enum constant When.MAYBE
  reason: class file for javax.annotation.meta.When not found
2 warnings

> Task :spring-beans:compileTestJava
Note: Some input files use unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.