patch 9.0.0063: too many type casts for dict_get functions

Problem:    Too many type casts for dict_get functions.
Solution:   Change the key argument from "char_u *" to "char *".
diff --git a/src/search.c b/src/search.c
index 3fd423f..2c045fe 100644
--- a/src/search.c
+++ b/src/search.c
@@ -4115,7 +4115,7 @@
 	    if (error)
 		return;
 	}
-	recompute = dict_get_bool(dict, (char_u *)"recompute", recompute);
+	recompute = dict_get_bool(dict, "recompute", recompute);
 	di = dict_find(dict, (char_u *)"pattern", -1);
 	if (di != NULL)
 	{
@@ -4645,7 +4645,8 @@
 	    // For a dict, either use the specified key to lookup the string or
 	    // use the specified callback function to get the string.
 	    if (key != NULL)
-		itemstr = dict_get_string(li->li_tv.vval.v_dict, key, FALSE);
+		itemstr = dict_get_string(li->li_tv.vval.v_dict,
+							   (char *)key, FALSE);
 	    else
 	    {
 		typval_T	argv[2];