TST - CI fails when importing from ``benchmark_utils``

Throughout https://github.com/benchopt/benchmark_sqrt_lasso/pull/3,
There seemed to be an issue with importing from ``benchmark_utils`` folder in the CI test.

From the error log,
```shell
File "benchmark_utils/__init__.py", line 2, in
from numba import njit
ModuleNotFoundError: No module named 'numba'
```

it appears that `benchopt` imports utils before installing the corresponding packages.
However, [benchmark bilevel](https://github.com/benchopt/benchmark_bilevel/blob/main/benchmark_utils/numba_utils.py) has the same case yet it successfully passes the CI tests.

Start with benchmark_utils/__init__.py and the CI error showing that numba is imported before it is available. Compare this setup with benchmark_bilevel's benchmark_utils/numba_utils.py and inspect the CI configuration; done means the benchmark's CI tests pass without the ModuleNotFoundError.

Written by the indexing model from the issue text.