fix: variant mapper g_to_t used wrong logic

[codecov[bot]]

Codecov Report

Patch coverage: 50.00% and project coverage change: +0.01 :tada:

Comparison is base (7f925c8) 86.00% compared to head (d647836) 86.01%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #32 +/- ## ========================================== + Coverage 86.00% 86.01% +0.01% ========================================== Files 17 17 Lines 6195 6194 -1 ========================================== Hits 5328 5328 + Misses 867 866 -1 ``` | [Impacted Files](https://codecov.io/gh/bihealth/hgvs-rs/pull/32?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=bihealth) | Coverage Δ | | |---|---|---| | [src/mapper/variant.rs](https://codecov.io/gh/bihealth/hgvs-rs/pull/32?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=bihealth#diff-c3JjL21hcHBlci92YXJpYW50LnJz) | `83.10% <50.00%> (-0.03%)` | :arrow_down: | | [src/parser/ds.rs](https://codecov.io/gh/bihealth/hgvs-rs/pull/32?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=bihealth#diff-c3JjL3BhcnNlci9kcy5ycw==) | `64.31% <0.00%> (+0.44%)` | :arrow_up: | 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 at Codecov.
:loudspeaker: Do you have feedback about the report comment? Let us know in this issue.