patch 8.2.3401: Vim9: cannot use negative count with finddir() and findfile()

Problem:    Vim9: cannot use a negative count with finddir() and findfile().
Solution:   Adjust the return type. (closes #8776)
diff --git a/src/evalfunc.c b/src/evalfunc.c
index fd385fe..b3f69c1 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -1354,9 +1354,9 @@
     {"filter",		2, 2, FEARG_1,	    arg2_mapfilter,
 			ret_first_arg,	    f_filter},
     {"finddir",		1, 3, FEARG_1,	    arg3_string_string_number,
-			ret_string,	    f_finddir},
+			ret_any,	    f_finddir},
     {"findfile",	1, 3, FEARG_1,	    arg3_string_string_number,
-			ret_string,	    f_findfile},
+			ret_any,	    f_findfile},
     {"flatten",		1, 2, FEARG_1,	    arg2_list_any_number,
 			ret_list_any,	    f_flatten},
     {"flattennew",	1, 2, FEARG_1,	    arg2_list_any_number,