fix: fixing wrong validation assumption about insertions

[codecov[bot]]

Codecov Report

Patch coverage has no change and project coverage change: -0.02 :warning:

Comparison is base (0a6a109) 88.32% compared to head (ad2d473) 88.30%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #64 +/- ## ========================================== - Coverage 88.32% 88.30% -0.02% ========================================== Files 19 19 Lines 7454 7450 -4 ========================================== - Hits 6584 6579 -5 - Misses 870 871 +1 ``` | [Impacted Files](https://codecov.io/gh/bihealth/hgvs-rs/pull/64?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/64?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: | ... and [1 file with indirect coverage changes](https://codecov.io/gh/bihealth/hgvs-rs/pull/64/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=bihealth) 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)

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