Assert while parsing valid yaml with ':' in text

While parsing:

```
value:
  description:
    Timecode in "HH:MM:SS:FF" format where the last ':' can be replaced by ',' or ';'.
```

rapidyam 0.5.0 asserts in `csubstr Parser::_consume_scalar()`, on `RYML_CHECK(m_state->flags & SSCL);`.

YAML contains tricky ":" in text string but is considered valid by online validators and is read correctly by libyaml.