chore: add vendor dependencies for kauma build

vendor/syn/tests/test_asyncness.rs

@@ -0,0 +1,43 @@
+#![allow(clippy::uninlined_format_args)]
+
+#[macro_use]
+mod macros;
+
+use syn::{Expr, Item};
+
+#[test]
+fn test_async_fn() {
+    let input = "async fn process() {}";
+
+    snapshot!(input as Item, @r###"
+    Item::Fn {
+        vis: Visibility::Inherited,
+        sig: Signature {
+            asyncness: Some,
+            ident: "process",
+            generics: Generics,
+            output: ReturnType::Default,
+        },
+        block: Block {
+            stmts: [],
+        },
+    }
+    "###);
+}
+
+#[test]
+fn test_async_closure() {
+    let input = "async || {}";
+
+    snapshot!(input as Expr, @r###"
+    Expr::Closure {
+        asyncness: Some,
+        output: ReturnType::Default,
+        body: Expr::Block {
+            block: Block {
+                stmts: [],
+            },
+        },
+    }
+    "###);
+}