fix: fixing wrong validation assumption about insertions

[codecov[bot]]

Codecov Report

Patch coverage has no change and project coverage change: -0.01 :warning:

Comparison is base (0a6a109) 88.32% compared to head (ad2d473) 88.32%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #62 +/- ## ========================================== - Coverage 88.32% 88.32% -0.01% ========================================== Files 19 19 Lines 7454 7449 -5 ========================================== - Hits 6584 6579 -5 Misses 870 870 ``` | [Impacted Files](https://codecov.io/gh/bihealth/hgvs-rs/pull/62?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=bihealth) | Coverage Δ | | |---|---|---| | [src/parser/impl\_validate.rs](https://codecov.io/gh/bihealth/hgvs-rs/pull/62?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=bihealth#diff-c3JjL3BhcnNlci9pbXBsX3ZhbGlkYXRlLnJz) | `83.52% <ø> (-0.92%)` | :arrow_down: | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=bihealth). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=bihealth)

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Do you have feedback about the report comment? Let us know in this issue.