fix: public load_auth() fn always called with include_env_var=true (#1961)

Apparently `include_env_var=false` was only used for testing, so clean
up the API a little to make that clear.


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* #1962
* __->__ #1961

codex-rs/tui/src/lib.rs

@@ -304,7 +304,7 @@ fn should_show_login_screen(config: &Config) -> bool {
         // Reading the OpenAI API key is an async operation because it may need
         // to refresh the token. Block on it.
         let codex_home = config.codex_home.clone();
-        match load_auth(&codex_home, true) {
+        match load_auth(&codex_home) {
             Ok(Some(_)) => false,
             Ok(None) => true,
             Err(err) => {