[FIX] skip newlines when reading FASTA with char.

[smehringer]

This error was introduced by https://github.com/seqan/seqan3/pull/3104

Fixes #3126

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Name	Status	Preview	Comments	Updated
seqan3	✅ Ready (Inspect)	Visit Preview	💬 Add your feedback	Jan 26, 2023 at 8:20AM (UTC)

[codecov[bot]]

Codecov Report

Base: 98.18% // Head: 98.18% // No change to project coverage :thumbsup:

Coverage data is based on head (00ab017) compared to base (58c5e18). Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #3127 +/- ## ======================================= Coverage 98.18% 98.18% ======================================= Files 276 276 Lines 12292 12292 ======================================= Hits 12069 12069 Misses 223 223 ``` | [Impacted Files](https://codecov.io/gh/seqan/seqan3/pull/3127?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=seqan) | Coverage Δ | | |---|---|---| | [include/seqan3/io/sequence\_file/format\_fasta.hpp](https://codecov.io/gh/seqan/seqan3/pull/3127?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=seqan#diff-aW5jbHVkZS9zZXFhbjMvaW8vc2VxdWVuY2VfZmlsZS9mb3JtYXRfZmFzdGEuaHBw) | `95.65% <100.00%> (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=seqan). 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=seqan)

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