docs: fix improved branin benchmark and run this example while building

[codecov[bot]]

Codecov Report

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

Comparison is base (1e0848e) 65.27% compared to head (b4bc397) 77.93%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #453 +/- ## =========================================== + Coverage 65.27% 77.93% +12.65% =========================================== Files 23 23 Lines 3145 3154 +9 =========================================== + Hits 2053 2458 +405 + Misses 1092 696 -396 ```

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