patch 9.0.1266: error for space before ": type" is inconsistent

Problem:    Error for space before ": type" is inconsistent.
Solution:   Give E1059 in more places. (closes #11868)

src/testdir/test_vim9_assign.vim

@@ -360,6 +360,13 @@ def Test_null_values()
   v9.CheckDefAndScriptSuccess(lines)
 enddef
 
+def Test_type_with_extra_white()
+  var lines =<< trim END
+      const x : number = 3
+  END
+  v9.CheckDefExecAndScriptFailure(lines, 'E1059')
+enddef
+
 def Test_keep_type_after_assigning_null()
   var lines =<< trim END
       var b: blob