patch 8.2.0855: GUI tests fail because the test doesn't use a modifier

Problem:    GUI tests fail because the test doesn't use a modifier.
Solution:   Add "\{xxx}" to be able to encode a modifier.
diff --git a/src/highlight.c b/src/highlight.c
index 7a7e537..9da87f2 100644
--- a/src/highlight.c
+++ b/src/highlight.c
@@ -1412,8 +1412,7 @@
 		 */
 		for (p = arg, off = 0; off < 100 - 6 && *p; )
 		{
-		    len = trans_special(&p, buf + off, FALSE, FALSE,
-								   TRUE, NULL);
+		    len = trans_special(&p, buf + off, FSK_SIMPLIFY, NULL);
 		    if (len > 0)	    // recognized special char
 			off += len;
 		    else		    // copy as normal char