goto-cc fails to parse enum/struct/unions with C23 attribute sequences

For example, the following code fails to parse:

```c
enum [[nodiscard]] error_t {
  A,
};

int main() {
}
```

The error output is:

```
test.c:2:1: error: syntax error before '['
 enum [[nodiscard]] error_t {
PARSING ERROR
```

This also fails in the exact same way for structs or unions with an attribute sequence.