patch 9.0.0219: cannot make a funcref with "s:func" in a def function

Problem:    Cannot make a funcref with "s:func" in a def function in legacy
            script.
Solution:   Allow for using a lower case function name after "s:". (Kota Kato,
            closes #10926)

src/testdir/test_vim9_func.vim

@@ -1957,6 +1957,45 @@ def Test_call_funcref()
     g:listarg->assert_equal([1, 2, 3])
   END
   v9.CheckScriptSuccess(lines)
+
+  lines =<< trim END
+    function s:func(num)
+      return a:num * 2
+    endfunction
+
+    def s:CallFuncref()
+      var Funcref = function('s:func')
+      Funcref(3)->assert_equal(6)
+    enddef
+    call s:CallFuncref()
+  END
+  v9.CheckScriptSuccess(lines)
+
+  lines =<< trim END
+    function s:func(num)
+      return a:num * 2
+    endfunction
+
+    def s:CallFuncref()
+      var Funcref = function(s:func)
+      Funcref(3)->assert_equal(6)
+    enddef
+    call s:CallFuncref()
+  END
+  v9.CheckScriptSuccess(lines)
+
+  lines =<< trim END
+    function s:func(num)
+      return a:num * 2
+    endfunction
+
+    def s:CallFuncref()
+      var Funcref = s:func
+      Funcref(3)->assert_equal(6)
+    enddef
+    call s:CallFuncref()
+  END
+  v9.CheckScriptSuccess(lines)
 enddef
 
 let SomeFunc = function('len')