Fix validation test for Java 15 (#1052)

With second preview the constructors of records now get the same access
modifier than the class (see JDK-8242479).

For "record WithoutFields" this leads to an private empty default
constructor which is filtered out by PrivateEmptyNoArgConstructorFilter.

Removing private modifiers from records to have consistent results
between first and second preview.

org.jacoco.core.test.validation.java14/src/org/jacoco/core/test/validation/java14/targets/RecordsTarget.java

@@ -17,15 +17,15 @@
  */
 public class RecordsTarget {
 
-	private record WithoutFields() { // assertFullyCovered()
+	record WithoutFields() { // assertFullyCovered()
 	}
 
-	private record WithFields( // assertPartlyCovered()
+	record WithFields( // assertPartlyCovered()
 			int x // assertEmpty()
 	) {
 	}
 
-	private record WithCustomMethods(int x) { // assertFullyCovered()
+	record WithCustomMethods(int x) { // assertFullyCovered()
 		public int x() {
 			return x; // assertNotCovered()
 		}