fix: staticcheck issues

Author: Stebalien

limit_test.go

@@ -22,4 +22,7 @@ func TestLimitWriter(t *testing.T) {
 		t.Fatal("Expected to write 3 bytes with no errors")
 	}
 	err = writer.Flush()
+	if err != nil {
+		t.Fatal(err)
+	}
 }

msgio_test.go

@@ -60,8 +60,7 @@ type testIoReadWriter struct {
 
 func TestReadWriterClose(t *testing.T) {
 	r, w := io.Pipe()
-	var rw ReadWriteCloser
-	rw = NewReadWriter(testIoReadWriter{r, w})
+	rw := NewReadWriter(testIoReadWriter{r, w})
 	SubtestReaderWriterClose(t, rw)
 }