Add a test fixture for a crate with a proc macro dependency

Author: Shnatsel

cargo-auditable/tests/fixtures/proc-macro-dependency/Cargo.lock

@@ -0,0 +1,9 @@
+[package]
+name = "proc-macro-dependency"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+serde = { version = "1.0.219", features = ["derive"] }
+
+[workspace]

cargo-auditable/tests/fixtures/proc-macro-dependency/Cargo.toml

@@ -0,0 +1,8 @@
+use serde::{Deserialize, Serialize};
+
+fn main() {
+    println!("{:?}", Hello("Hello, world!"));
+}
+
+#[derive(Serialize, Deserialize, Debug)]
+struct Hello (&'static str);