Fix CI testing

Author: alexcrichton

.github/workflows/main.yml

@@ -68,7 +68,9 @@ jobs:
 
     # Deny warnings on CI to avoid warnings getting into the codebase.
     - run: cargo test --features 'deny-warnings'
-    - run: cargo test --features 'deny-warnings' -p cargo-test-support
+    - run: cargo test --features 'deny-warnings' --manifest-path crates/cargo-test-support/Cargo.toml
+      env:
+        CARGO_TARGET_DIR: target
     - run: cargo test -p cargo-platform
     - run: cargo test -p cargo-util
     - run: cargo test --manifest-path crates/mdman/Cargo.toml

crates/cargo-test-support/Cargo.toml

@@ -23,3 +23,6 @@ tar = { version = "0.4.18", default-features = false }
 termcolor = "1.1.2"
 toml = "0.5.7"
 url = "2.2.2"
+
+[features]
+deny-warnings = []

crates/cargo-test-support/src/lib.rs

@@ -5,6 +5,7 @@
 #![allow(clippy::all)]
 #![warn(clippy::needless_borrow)]
 #![warn(clippy::redundant_clone)]
+#![cfg_attr(feature = "deny-warnings", deny(warnings))]
 
 use std::env;
 use std::ffi::OsStr;