tests: fix fiber status detection

Author: 0x501D

t/020-fifottl.t

@@ -217,8 +217,7 @@ test:test('read_only test', function(test)
     local rc = queue_state.poll_waiting(10)
     test:ok(rc, "queue state changed to waiting")
     fiber.sleep(0.11)
-    local _, err = pcall(ttl_fiber.info, ttl_fiber)
-    test:is(err, "the fiber is dead",
+    test:is(ttl_fiber:status(), 'dead',
         "check that background fiber is canceled")
     test:isnil(tube.raw.fiber,
             "check that background fiber object is cleaned")

t/040-utubettl.t

@@ -229,8 +229,7 @@ test:test('read_only test', function(test)
     local rc = queue_state.poll_waiting(10)
     test:ok(rc, "queue state changed to waiting")
     fiber.sleep(0.11)
-    local _, err = pcall(ttl_fiber.info, ttl_fiber)
-    test:is(err, "the fiber is dead",
+    test:is(ttl_fiber:status(), 'dead',
         "check that background fiber is canceled")
     test:isnil(tube.raw.fiber,
             "check that background fiber object is cleaned")