patch 9.0.1831: Vim9: failing null test

Problem:  Vim9: failing null test
Solution: Use required public keyword

closes: #12982

Signed-off-by: Christian Brabandt <[email protected]>
Co-authored-by: Gianmaria Bajo <[email protected]>

Author: mg979

src/testdir/test_vim9_class.vim

@@ -1184,7 +1184,7 @@ def Test_class_member()
   lines =<< trim END
     vim9script
     class A
-        this.val: string
+        public this.val: string
     endclass
 
     def F()
@@ -1214,7 +1214,7 @@ def Test_class_member()
   lines =<< trim END
     vim9script
     class A
-        this.val: string
+        public this.val: string
     endclass
 
     var obj: A

src/version.c

@@ -699,6 +699,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1831,
 /**/
     1830,
 /**/