Work around rust-lang/rust#131729

Author: smoelius

tests/ci.rs

@@ -6,6 +6,9 @@ use tempfile::tempdir;
 #[test]
 fn clippy() {
     Command::new("cargo")
+        // smoelius: Remove `CARGO` environment variable to work around:
+        // https://github.com/rust-lang/rust/pull/131729
+        .env_remove("CARGO")
         .args([
             "+nightly",
             "clippy",