fix(test-support): use CARGO_BUILD_TARGET_DIR env var (#15212)

# Description

cargo uses both CARGO_BUILD_TARGET_DIR and CARGO_TARGET_DIR, so check
for CARGO_BUILD_TARGET_DIR if CARGO_TARGET_DIR is not found

https://doc.rust-lang.org/cargo/reference/config.html#buildtarget-dir

crates/nu-test-support/src/fs.rs

@@ -88,6 +88,7 @@ pub fn binaries() -> AbsolutePathBuf {
     };
 
     std::env::var("CARGO_TARGET_DIR")
+        .or_else(|_| std::env::var("CARGO_BUILD_TARGET_DIR"))
         .ok()
         .and_then(|p| AbsolutePathBuf::try_from(p).ok())
         .unwrap_or_else(|| root().join("target"))