patch 8.2.0898: missing help for a function goes unnoticed

Problem:    Missing help for a function goes unnoticed.
Solution:   Add a test. (Gary Johnson)
diff --git a/src/testdir/Make_all.mak b/src/testdir/Make_all.mak
index 7fad24b..6b151d0 100644
--- a/src/testdir/Make_all.mak
+++ b/src/testdir/Make_all.mak
@@ -139,6 +139,7 @@
 	test_fnamemodify \
 	test_fold \
 	test_functions \
+	test_function_lists \
 	test_ga \
 	test_getcwd \
 	test_getvar \
@@ -374,6 +375,7 @@
 	test_fnameescape.res \
 	test_fold.res \
 	test_functions.res \
+	test_function_lists.res \
 	test_getcwd.res \
 	test_getvar.res \
 	test_gf.res \