all: replace empty slice literal with var (#8990)

refactor: replace empty slice literal with `var`

An empty slice can be represented by `nil` or an empty slice literal. They are
functionally equivalent — their `len` and `cap` are both zero — but the `nil`
slice is the preferred style. For more information about empty slices,
see [Declaring Empty Slices](https://github.com/golang/go/wiki/CodeReviewComments#declaring-empty-slices).

Co-authored-by: deepsource-autofix[bot] <62050782+deepsource-autofix[bot]@users.noreply.github.com>

lib/model/model_test.go

@@ -1709,7 +1709,8 @@ func TestGlobalDirectoryTree(t *testing.T) {
 
 	b := func(isfile bool, path ...string) protocol.FileInfo {
 		typ := protocol.FileInfoTypeDirectory
-		blocks := []protocol.BlockInfo{}
+		var blocks []protocol.BlockInfo
+
 		if isfile {
 			typ = protocol.FileInfoTypeFile
 			blocks = []protocol.BlockInfo{{Offset: 0x0, Size: 0xa, Hash: []uint8{0x2f, 0x72, 0xcc, 0x11, 0xa6, 0xfc, 0xd0, 0x27, 0x1e, 0xce, 0xf8, 0xc6, 0x10, 0x56, 0xee, 0x1e, 0xb1, 0x24, 0x3b, 0xe3, 0x80, 0x5b, 0xf9, 0xa9, 0xdf, 0x98, 0xf9, 0x2f, 0x76, 0x36, 0xb0, 0x5c}}}