doc: fix duplicate "the" in sequence dictionary docstrings

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 95.62%. Comparing base (8d31cf3) to head (a74b8f8). Report is 1 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1000 +/- ## ======================================= Coverage 95.62% 95.62% ======================================= Files 126 126 Lines 7364 7364 Branches 500 500 ======================================= Hits 7042 7042 Misses 322 322 ``` | [Flag](https://app.codecov.io/gh/fulcrumgenomics/fgbio/pull/1000/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=fulcrumgenomics) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/fulcrumgenomics/fgbio/pull/1000/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=fulcrumgenomics) | `95.62% <ø> (ø)` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=fulcrumgenomics#carryforward-flags-in-the-pull-request-comment) to find out more.

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