Liftover failure leads to duplicate Alleles, tags not showing

Create variant:

NC_000007.14:g.140753336_140763336del

Then tag. This kicks off ```variant_tag_created_task```

There are dupe alleles made:

```
In [10]: for v in VariantAllele.objects.filter(variant=variant_tag.variant, genome_build=variant_tag.genome_build).values("variant", "genome_build", "a
...: llele"):
...: print(v)
...:
{'variant': 14601769, 'genome_build': 'GRCh38', 'allele': 1146}
{'variant': 14601769, 'genome_build': 'GRCh38', 'allele': 1147}
{'variant': 14601769, 'genome_build': 'GRCh38', 'allele': 1148}
{'variant': 14601769, 'genome_build': 'GRCh38', 'allele': 1149}
```