Polish ImportsContextCustomizerTests

Update the test classes to include an `@Import` annotation. Without this
the tests would not fail even if the filter is missing.

spring-boot-project/spring-boot-test/src/test/java/org/springframework/boot/test/context/ImportsContextCustomizerTests.java

@@ -105,31 +105,37 @@ class ImportsContextCustomizerTests {
 	}
 
 	@Metadata(d2 = "foo")
+	@Import(TestImportSelector.class)
 	static class FirstKotlinAnnotatedTestClass {
 
 	}
 
 	@Metadata(d2 = "bar")
+	@Import(TestImportSelector.class)
 	static class SecondKotlinAnnotatedTestClass {
 
 	}
 
 	@SpecMetadata(filename = "foo", line = 10)
+	@Import(TestImportSelector.class)
 	static class FirstSpockFrameworkAnnotatedTestClass {
 
 	}
 
 	@SpecMetadata(filename = "bar", line = 10)
+	@Import(TestImportSelector.class)
 	static class SecondSpockFrameworkAnnotatedTestClass {
 
 	}
 
 	@Stepwise
+	@Import(TestImportSelector.class)
 	static class FirstSpockLangAnnotatedTestClass {
 
 	}
 
 	@Issue("1234")
+	@Import(TestImportSelector.class)
 	static class SecondSpockLangAnnotatedTestClass {
 
 	}