Fix tar duplicate artifact in rust-lang/rust.

Author: ehuss

crates/cargo-test-support/Cargo.toml

@@ -17,5 +17,5 @@ glob = "0.3"
 lazy_static = "1.0"
 remove_dir_all = "0.5"
 serde_json = "1.0"
-tar = "0.4"
+tar = { version = "0.4.18", default-features = false }
 url = "2.0"