Typo fix in error message (add missing word)

[codecov-commenter]

Codecov Report

Patch and project coverage have no change.

Comparison is base (e6c7a30) 86.70% compared to head (50d7f61) 86.70%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #351 +/- ## ======================================= Coverage 86.70% 86.70% ======================================= Files 18 18 Lines 2143 2143 ======================================= Hits 1858 1858 Misses 285 285 ``` | [Impacted Files](https://codecov.io/gh/iterative/gto/pull/351?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=iterative) | Coverage Δ | | |---|---|---| | [gto/constants.py](https://codecov.io/gh/iterative/gto/pull/351?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=iterative#diff-Z3RvL2NvbnN0YW50cy5weQ==) | `100.00% <ø> (ø)` | | 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=iterative). 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=iterative)

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