patch 8.1.1004: function "luaV_setref()" not covered with tests

Problem:    Function "luaV_setref()" not covered with tests.
Solution:   Add a test. (Dominique Pelle, closes #4089)
diff --git a/src/testdir/test_lua.vim b/src/testdir/test_lua.vim
index 1a5c74f..7fcdad5 100644
--- a/src/testdir/test_lua.vim
+++ b/src/testdir/test_lua.vim
@@ -4,6 +4,11 @@
   finish
 endif
 
+func TearDown()
+  " Run garbage collection after each test to exercise luaV_setref().
+  call test_garbagecollect_now()
+endfunc
+
 " Check that switching to another buffer does not trigger ml_get error.
 func Test_command_new_no_ml_get_error()
   new
diff --git a/src/version.c b/src/version.c
index 5b16760..0b0ab0c 100644
--- a/src/version.c
+++ b/src/version.c
@@ -780,6 +780,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1004,
+/**/
     1003,
 /**/
     1002,