fix: correct mutex unlock in IsClosed.Err() method> (#129)

* fix: correct mutex unlock in IsClosed.Err() method>
* extend test to catch this problem in the future

---------

Co-authored-by: ilia.sergunin <[email protected]>

Author: honeynil

trm/drivers/is_closed.go

@@ -70,7 +70,7 @@ func (a *IsClosed) CloseWithCause(err error) {
 // Err is inspired function Err in https://pkg.go.dev/context#Context
 func (a *IsClosed) Err() error {
 	a.mu.RLock()
-	defer a.mu.RLock()
+	defer a.mu.RUnlock()
 
 	return a.err
 }

trm/drivers/is_closed_test.go

@@ -18,6 +18,7 @@ func TestIsClose(t *testing.T) {
 
 	require.True(t, isClosed.IsActive())
 	require.False(t, isClosed.IsClosed())
+	require.NoError(t, isClosed.Err())
 
 	wg := sync.WaitGroup{}