Fix incorrect VC default HTTP token path when the --datadir flag is present (#6748)

* Fix incorrect default http token path when datadir flag is present.

lighthouse/tests/validator_client.rs

@@ -345,7 +345,7 @@ fn http_store_keystore_passwords_in_secrets_dir_present() {
 }
 
 #[test]
-fn http_token_path_flag() {
+fn http_token_path_flag_present() {
     let dir = TempDir::new().expect("Unable to create temporary directory");
     CommandLineTest::new()
         .flag("http", None)
@@ -359,6 +359,19 @@ fn http_token_path_flag() {
         });
 }
 
+#[test]
+fn http_token_path_default() {
+    CommandLineTest::new()
+        .flag("http", None)
+        .run()
+        .with_config(|config| {
+            assert_eq!(
+                config.http_api.http_token_path,
+                config.validator_dir.join("api-token.txt")
+            );
+        });
+}
+
 // Tests for Metrics flags.
 #[test]
 fn metrics_flag() {