Reinstate running of OutputCaptureRuleTests

See gh-19826

spring-boot-project/spring-boot-test/build.gradle

@@ -52,4 +52,10 @@ dependencies {
 	testImplementation 'org.testng:testng'
 
 	testRuntimeOnly 'org.junit.platform:junit-platform-launcher'
-}
+	testRuntimeOnly 'org.junit.vintage:junit-vintage-engine'
\ No newline at end of file
+}
+
+test {
+	useJUnit()
+	useJUnitPlatform()
+}