chore: replace some missing() with is_missing()

[maelle]

Fix #2402

[github-actions]

This is how benchmark results would change (along with a 95% confidence interval in relative change) if 59faa94 is merged into main:

• ✔️as_adjacency_matrix: 782ms -> 771ms [-3.39%, +0.61%]
• ✔️as_biadjacency_matrix: 755ms -> 756ms [-0.43%, +0.87%]
• ✔️as_data_frame_both: 1.71ms -> 1.73ms [-3.34%, +4.92%]
• ✔️as_long_data_frame: 4.14ms -> 4.15ms [-1.45%, +2.35%]
• ✔️es_attr_filter: 2.75ms -> 2.72ms [-2.67%, +0.3%]
• ✔️graph_from_adjacency_matrix: 122ms -> 123ms [-1.19%, +1.97%]
• ✔️graph_from_data_frame: 3.89ms -> 3.87ms [-2.94%, +2.34%]
• ✔️vs_attr_filter: 1.55ms -> 1.63ms [-5.36%, +15.3%]
• ✔️vs_by_name: 1.01ms -> 1.02ms [-2.08%, +3.48%]
  Further explanation regarding interpretation and methodology can be found in the documentation.

[github-actions]

This is how benchmark results would change (along with a 95% confidence interval in relative change) if ccb0227 is merged into main:

• ✔️as_adjacency_matrix: 891ms -> 889ms [-2.2%, +1.75%]
• ✔️as_biadjacency_matrix: 873ms -> 869ms [-2.21%, +1.29%]
• ✔️as_data_frame_both: 1.93ms -> 1.93ms [-1.26%, +1.78%]
• ✔️as_long_data_frame: 4.58ms -> 4.57ms [-3.33%, +2.86%]
• ✔️es_attr_filter: 3.18ms -> 3.19ms [-2.65%, +3.73%]
• ✔️graph_from_adjacency_matrix: 173ms -> 169ms [-5.09%, +1.03%]
• ✔️graph_from_data_frame: 4.12ms -> 4.13ms [-1.5%, +1.98%]
• ✔️vs_attr_filter: 1.77ms -> 1.78ms [-3.56%, +4.11%]
• ✔️vs_by_name: 1.28ms -> 1.28ms [-2.78%, +2.22%]
  Further explanation regarding interpretation and methodology can be found in the documentation.