fix core::config::tests::override_toml

Signed-off-by: onur-ozkan <work@onurozkan.dev>

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

@@ -135,6 +135,7 @@ fn override_toml() {
 [rust]
 lto = "off"
 deny-warnings = true
+download-rustc=false
 
 [build]
 gdb = "foo"
@@ -200,6 +201,8 @@ fn override_toml() {
             .collect(),
         "setting dictionary value"
     );
+    assert!(!config.llvm_from_ci);
+    assert!(!config.download_rustc());
 }
 
 #[test]