### 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)

return mode;
}
void FileDialog::set_access(Access p_access) {
	ERR_FAIL_INDEX(p_access, 3);
	if (access == p_access) {
		return;
	}
	switch (p_access) {
		case ACCESS_FILESYSTEM: {
			dir_access = DirAccess::create(DirAccess::ACCESS_FILESYSTEM);
		} break;
		case ACCESS_RESOURCES: {
			dir_access = DirAccess::create(DirAccess::ACCESS_RESOURCES);
		} break;
		case ACCESS_USERDATA: {
			dir_access = DirAccess::create(DirAccess::ACCESS_USERDATA);
		} break;
	}
	access = p_access;
	root_prefix = "";
	root_subfolder = "";
	_update_drives();
	invalidate();
	update_filters();
	update_dir();
}
void FileDialog::invalidate() {