patch 8.1.2156: first character after Tab is not highlighted

Problem:    First character after Tab is not highlighted.
Solution:   Remember the syntax attribute for a column.
diff --git a/src/testdir/test_syntax.vim b/src/testdir/test_syntax.vim
index 0479901..c7d6f2d 100644
--- a/src/testdir/test_syntax.vim
+++ b/src/testdir/test_syntax.vim
@@ -551,10 +551,10 @@
 	\ '}',
 	\ '   static void',
 	\ 'myFunction(const double count, struct nothing, long there) {',
-	\ '  // 123: nothing to read here',
-	\ '  for (int i = 0; i < count; ++i) {',
-	\ '    break;',
-	\ '  }',
+	\ "\t// 123: nothing to read here",
+	\ "\tfor (int i = 0; i < count; ++i) {",
+	\ "\t   break;",
+	\ "\t}",
 	\ '}',
 	\ ], 'Xtest.c')