Disable class data sharing (CDS) for tests

Prior to this commit, the Gradle build output the following warning
multiple times.

OpenJDK 64-Bit Server VM warning: Sharing is only supported for boot loader classes because bootstrap classpath has been appended

Since we don't need CDS enabled for our tests, I've added `-Xshare:off`
as a JVM argument for our tests to disable CDS.

buildSrc/src/main/java/org/springframework/build/TestConventions.java

@@ -64,7 +64,7 @@ private void configureTests(Project project, Test test) {
 		}
 		test.jvmArgs("--add-opens=java.base/java.lang=ALL-UNNAMED",
 				"--add-opens=java.base/java.util=ALL-UNNAMED",
-				"-Djava.locale.providers=COMPAT");
+				"-Djava.locale.providers=COMPAT", "-Xshare:off");
 	}
 
 	private void configureTestRetryPlugin(Project project, Test test) {