local: fix TestRemoveThroughPlantedSymlinkBlocked failing on Windows

On Windows os.Root.Symlink always makes a file symlink when the
target is an absolute path outside the root, and Windows can't
traverse a file symlink as a directory. The planted link can't reach
the outside files, so the test failed setting up the attack with "The
filename, directory name, or volume label syntax is incorrect".

Skip the test on Windows as the other planted symlink tests do.

backend/local/local_internal_test.go

@@ -597,6 +597,12 @@ func TestMkdirMetadataThroughPlantedSymlinkBlocked(t *testing.T) {
 // TestRemoveThroughPlantedSymlinkBlocked checks Remove and Rmdir can't
 // delete anything outside the root through a planted symlink.
 func TestRemoveThroughPlantedSymlinkBlocked(t *testing.T) {
+	if runtime.GOOS == "windows" {
+		// os.Root.Symlink makes a file symlink to a directory outside
+		// the root, which Windows can't traverse, so the planted link
+		// can't reach the outside files.
+		t.Skip("planted directory symlinks can't be traversed on Windows")
+	}
 	skipIfNoSymlinks(t)
 	ctx := context.Background()