update_cached_repo(): Actually update.

src/git.cpp

@@ -253,6 +253,7 @@ void update_cached_repo()
     check(git_checkout_options_init(&checkout_opts,
                                     GIT_CHECKOUT_OPTIONS_VERSION));
     checkout_opts.checkout_strategy = GIT_CHECKOUT_FORCE;
+    check(git_repository_set_head(_repo, "refs/heads/main"));
     check(git_checkout_head(_repo, &checkout_opts));
 
     git_remote_free(remote);