build: fix linting issues reported by running golangci-lint with different GOOS

vfs/vfstest/write_other.go

@@ -0,0 +1,20 @@
+//go:build !linux && !darwin && !freebsd && !windows
+// +build !linux,!darwin,!freebsd,!windows
+
+package vfstest
+
+import (
+	"errors"
+	"runtime"
+	"testing"
+)
+
+// TestWriteFileDoubleClose tests double close on write
+func TestWriteFileDoubleClose(t *testing.T) {
+	t.Skip("not supported on " + runtime.GOOS)
+}
+
+// writeTestDup performs the platform-specific implementation of the dup() unix
+func writeTestDup(oldfd uintptr) (uintptr, error) {
+	return 0, errors.New("not supported on " + runtime.GOOS)
+}