Make generate no-args constructor package private

The idea here is that hopefully it convince code coverage
tools to ignore it

Relates to: quarkusio#32254

independent-projects/arc/processor/src/main/java/io/quarkus/arc/processor/Beans.java

@@ -1040,7 +1040,7 @@ public void visit(int version, int access, String name, String signature,
                         String superName,
                         String[] interfaces) {
                     super.visit(version, access, name, signature, superName, interfaces);
-                    MethodVisitor mv = visitMethod(Modifier.PUBLIC | Opcodes.ACC_SYNTHETIC, Methods.INIT, "()V", null,
+                    MethodVisitor mv = visitMethod(Opcodes.ACC_SYNTHETIC, Methods.INIT, "()V", null,
                             null);
                     mv.visitCode();
                     mv.visitVarInsn(Opcodes.ALOAD, 0);