update cargo during test

Author: Shourya742

src/bootstrap/src/core/config/config.rs

@@ -503,7 +503,7 @@ impl Config {
             host: build_host_toml,
             target: build_target_toml,
             build_dir: build_build_dir_toml,
-            cargo: build_cargo_toml,
+            cargo: mut build_cargo_toml,
             rustc: mut build_rustc_toml,
             rustfmt: build_rustfmt_toml,
             cargo_clippy: build_cargo_clippy_toml,
@@ -672,9 +672,8 @@ impl Config {
             // Cargo in their bootstrap.toml.
             build_rustc_toml =
                 build_rustc_toml.take().or(std::env::var_os("RUSTC").map(|p| p.into()));
-            build_build_toml = build_build_toml
-                .take()
-                .or(std::env::var_os("CARGO").map(|p| p.into_string().unwrap()));
+            build_cargo_toml =
+                build_cargo_toml.take().or(std::env::var_os("CARGO").map(|p| p.into()));
         }
 
         build_jobs_toml = flags_jobs.or(build_jobs_toml);