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.

(cherry picked from commit 27985b1439)

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

@@ -62,8 +62,11 @@ class TestConventions {
 		if (project.hasProperty("testGroups")) {
 			test.systemProperty("testGroups", project.getProperties().get("testGroups"));
 		}
-		test.jvmArgs("--add-opens=java.base/java.lang=ALL-UNNAMED",
-				"--add-opens=java.base/java.util=ALL-UNNAMED");
+		test.jvmArgs(
+				"--add-opens=java.base/java.lang=ALL-UNNAMED",
+				"--add-opens=java.base/java.util=ALL-UNNAMED",
+				"-Xshare:off"
+		);
 	}
 
 	private void configureTestRetryPlugin(Project project, Test test) {