patch 9.0.1280: inssufficient testing for what 9.0.1265 fixes

Problem:    Inssufficient testing for what 9.0.1265 fixes.
Solution:   Add a couple of test cases. (issue #11885)

src/testdir/test_vim9_class.vim

@@ -1050,6 +1050,60 @@ def Test_call_interface_method()
   END
   v9.CheckScriptSuccess(lines)
 
+  # method of interface returns a value
+  lines =<< trim END
+    vim9script
+    interface Base
+      def Enter(): string
+    endinterface
+
+    class Child implements Base
+      def Enter(): string
+        g:result ..= 'child'
+        return "/resource"
+      enddef
+    endclass
+
+    def F(obj: Base)
+      var r = obj.Enter()
+      g:result ..= r
+    enddef
+
+    g:result = ''
+    F(Child.new())
+    assert_equal('child/resource', g:result)
+    unlet g:result
+  END
+  v9.CheckScriptSuccess(lines)
+
+  lines =<< trim END
+    vim9script
+    class Base
+      def Enter(): string
+        return null_string
+      enddef
+    endclass
+
+    class Child extends Base
+      def Enter(): string
+        g:result ..= 'child'
+        return "/resource"
+      enddef
+    endclass
+
+    def F(obj: Base)
+      var r = obj.Enter()
+      g:result ..= r
+    enddef
+
+    g:result = ''
+    F(Child.new())
+    assert_equal('child/resource', g:result)
+    unlet g:result
+  END
+  v9.CheckScriptSuccess(lines)
+
+
   # No class that implements the interface.
   lines =<< trim END
       vim9script

src/version.c

@@ -695,6 +695,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1280,
 /**/
     1279,
 /**/