### Godot version

v4.1.stable.official [970459615]

### System information

Windows 10

### Issue description

When changing the `file_mode` of `FileDialog` from "Open File" to "Save File" via code the "Save" button keeps disabled until a file or folder is selected if the "Open" button was disabled before.

Basically the button activity has to be updated when `file_mode` is changed. I have made the change already but the last time I opened an PR without an issue some people requested I open one. So here you are!

### Steps to reproduce

- Open the MRP and start it
- click anywere to open the dialog
- after 10 seconds the dialog changes file_mode
- if the button is disabled before the change it is as well after it

### Minimal reproduction project

[file_dialogue_test.zip](https://github.com/godotengine/godot/files/11991311/file_dialogue_test.zip)

break;
		case FILE_MODE_OPEN_DIR:
			set_ok_button_text(RTR("Select Current Folder"));
			if (mode_overrides_title) {
				set_title(TTRC("Open a Directory"));
			}
			makedir->show();
			break;
		case FILE_MODE_OPEN_ANY:
			set_ok_button_text(RTR("Open"));
			if (mode_overrides_title) {
				set_title(TTRC("Open a File or Directory"));
			}
			makedir->show();
			break;
		case FILE_MODE_SAVE_FILE:
			set_ok_button_text(RTR("Save"));
			if (mode_overrides_title) {
				set_title(TTRC("Save a File"));
			}
			makedir->show();
			break;
	}
	if (mode == FILE_MODE_OPEN_FILES) {
		tree->set_select_mode(Tree::SELECT_MULTI);
	} else {
		tree->set_select_mode(Tree::SELECT_SINGLE);
	}
}
FileDialog::FileMode FileDialog::get_file_mode() const {