Fix main branch name in documenter.yml

[codecov-commenter]

Codecov Report

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

Comparison is base (09c5d41) 85.60% compared to head (d9af53f) 85.60%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #633 +/- ## ======================================= Coverage 85.60% 85.60% ======================================= Files 45 45 Lines 3862 3862 ======================================= Hits 3306 3306 Misses 556 556 ```

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