registry: fix check_ref with full ref name

[pmrowla]

Will fix https://github.com/iterative/gto-action/issues/39

[codecov-commenter]

Codecov Report

Patch coverage: 100.00% and project coverage change: -0.01% :warning:

Comparison is base (7663159) 85.52% compared to head (169b9b2) 85.51%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #382 +/- ## ========================================== - Coverage 85.52% 85.51% -0.01% ========================================== Files 18 18 Lines 2121 2120 -1 ========================================== - Hits 1814 1813 -1 Misses 307 307 ``` | [Files Changed](https://app.codecov.io/gh/iterative/gto/pull/382?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=iterative) | Coverage Δ | | |---|---|---| | [gto/registry.py](https://app.codecov.io/gh/iterative/gto/pull/382?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=iterative#diff-Z3RvL3JlZ2lzdHJ5LnB5) | `90.53% <100.00%> (-0.04%)` | :arrow_down: |

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