Use better heuristic for printing Cargo specific diagnostics

compiler/rustc_parse/src/errors.rs

@@ -2545,7 +2545,7 @@ pub enum HelpUseLatestEdition {
 impl HelpUseLatestEdition {
     pub fn new() -> Self {
         let edition = LATEST_STABLE_EDITION;
-        if std::env::var_os("CARGO").is_some() {
+        if rustc_session::utils::was_invoked_from_cargo() {
             Self::Cargo { edition }
         } else {
             Self::Standalone { edition }