fix: auth.json leak in tests (#18657)

Before this some tests were leaking an auth.json file into
`codex-rs/core`. This just fixes it

codex-rs/login/src/auth/manager.rs

@@ -13,6 +13,8 @@ use std::path::PathBuf;
 use std::sync::Arc;
 use std::sync::Mutex;
 use std::sync::RwLock;
+use std::sync::atomic::AtomicU64;
+use std::sync::atomic::Ordering;
 use tokio::sync::Mutex as AsyncMutex;
 use tokio::sync::watch;
 
@@ -96,6 +98,7 @@ const REFRESH_TOKEN_URL: &str = "https://auth.openai.com/oauth/token";
 pub(super) const REVOKE_TOKEN_URL: &str = "https://auth.openai.com/oauth/revoke";
 pub const REFRESH_TOKEN_URL_OVERRIDE_ENV_VAR: &str = "CODEX_REFRESH_TOKEN_URL_OVERRIDE";
 pub const REVOKE_TOKEN_URL_OVERRIDE_ENV_VAR: &str = "CODEX_REVOKE_TOKEN_URL_OVERRIDE";
+static NEXT_DUMMY_AUTH_ID: AtomicU64 = AtomicU64::new(1);
 
 #[derive(Debug, Error)]
 pub enum RefreshTokenError {
@@ -442,7 +445,11 @@ impl CodexAuth {
             auth_dot_json: Arc::new(Mutex::new(Some(auth_dot_json))),
             client,
         };
-        let storage = create_auth_storage(PathBuf::new(), AuthCredentialsStoreMode::File);
+        let dummy_auth_id = NEXT_DUMMY_AUTH_ID.fetch_add(1, Ordering::Relaxed);
+        let storage = create_auth_storage(
+            PathBuf::from(format!("dummy-chatgpt-auth-{dummy_auth_id}")),
+            AuthCredentialsStoreMode::Ephemeral,
+        );
         Self::Chatgpt(ChatgptAuth { state, storage })
     }