docs: other roxygen2 warning

[maelle]

Or should it be Matrix::solve()?

[github-actions]

This is how benchmark results would change (along with a 95% confidence interval in relative change) if a1807de is merged into main:

• ✔️as_adjacency_matrix: 646ms -> 643ms [-1.78%, +0.93%]
• ✔️as_biadjacency_matrix: 668ms -> 662ms [-2.99%, +1.06%]
• ✔️as_data_frame_both: 1.33ms -> 1.34ms [-0.97%, +2.29%]
• ✔️as_long_data_frame: 3.23ms -> 3.23ms [-1.21%, +1.36%]
• ✔️es_attr_filter: 2.16ms -> 2.14ms [-3.1%, +1.11%]
• ✔️graph_from_adjacency_matrix: 134ms -> 135ms [-1.83%, +1.94%]
• ✔️graph_from_data_frame: 3.05ms -> 3.02ms [-2.65%, +1.22%]
• ✔️vs_attr_filter: 1.25ms -> 1.24ms [-2.71%, +1.58%]
• ✔️vs_by_name: 791µs -> 804µs [-0.42%, +3.63%]
  Further explanation regarding interpretation and methodology can be found in the documentation.