unit tests: Skip Windows-unrelated tests on Windows

Some of the unit tests cannot pass on Windows due to various reasons:

- fsnotify does not have a Windows implementation.
- Proxy Mode IPVS not supported on Windows.
- Seccomp not supported on Windows.
- VolumeMode=Block is not supported on Windows.
- iSCSI volumes are mounted differently on Windows, and iscsiadm is a
  Linux utility.

pkg/proxy/ipvs/proxier_test.go

@@ -1,3 +1,6 @@
+//go:build !windows
+// +build !windows
+
 /*
 Copyright 2017 The Kubernetes Authors.