Disable publication of test fixture artifacts

Thanks to @melix for providing the code snippet necessary to achieve
this with Gradle 5.6.x.

See gh-23550

gradle/spring-module.gradle

@@ -55,6 +55,14 @@ task javadocJar(type: Jar) {
 publishing {
 	publications {
 		mavenJava(MavenPublication) {
+			// Disable publication of test fixture artifacts.
+			//
+			// Once we upgrade to Gradle 6.x, we will need to delete the following line ...
+			components.java.variants.removeAll { it.outgoingConfiguration.name.startsWith("testFixtures") }
+			// ... and uncomment the following two lines.
+			// components.java.withVariantsFromConfiguration(configurations.testFixturesApiElements) { skip() }
+			// components.java.withVariantsFromConfiguration(configurations.testFixturesRuntimeElements) { skip() }
+
 			from components.java
 			artifact sourcesJar
 			artifact javadocJar