Add missing syn feature

Author: lnicola

src/tools/rust-analyzer/crates/query-group-macro/Cargo.toml

@@ -15,7 +15,7 @@ proc-macro = true
 [dependencies]
 proc-macro2 = "1.0"
 quote = "1.0"
-syn = { version = "2.0", features = ["full", "extra-traits"] }
+syn = { version = "2.0", features = ["full", "extra-traits", "visit-mut"] }
 
 [dev-dependencies]
 expect-test = "1.5.0"