chore: increase R minimal version to R4.0.0

[maelle]

I'll create a stack to go up to R4.1.0 in two more PRs, in case we decide to.

[github-actions]

This is how benchmark results would change (along with a 95% confidence interval in relative change) if 3d3ed53 is merged into main:

• ✔️as_adjacency_matrix: 867ms -> 878ms [-0.74%, +3.36%]
• ✔️as_biadjacency_matrix: 860ms -> 858ms [-3.79%, +3.23%]
• ✔️as_data_frame_both: 1.93ms -> 1.88ms [-9.98%, +4.44%]
• ✔️as_long_data_frame: 4.52ms -> 4.56ms [-2.44%, +3.98%]
• ✔️es_attr_filter: 2.76ms -> 2.74ms [-1.67%, +0.5%]
• ✔️graph_from_adjacency_matrix: 157ms -> 159ms [-1.79%, +5.45%]
• ✔️graph_from_data_frame: 4.29ms -> 4.19ms [-9.74%, +4.88%]
• ✔️vs_attr_filter: 1.62ms -> 1.6ms [-4.93%, +2.25%]
• ✔️vs_by_name: 1.01ms -> 1.01ms [-0.96%, +1.36%]
  Further explanation regarding interpretation and methodology can be found in the documentation.