Panic with CPython 3.9

# Reproducible command

```sh
poise init
```

# Result

```sh
/Users/shiba/.erg/bin/poise: line 1: 33964 Segmentation fault: 11  python3 /Users/shiba/.erg/bin/poise.pyc $@
```

# Version

CPython 3.9
Erg 0.6.31

# Note

This may be the bug of the Erg code generator.