Drop support for Python 3.7

[RobertCraigie]

It's past EOL and only ~1% of users are still using 3.7

pipx run pypistats python_minor prisma
┌──────────┬─────────┬───────────┐
│ category │ percent │ downloads │
├──────────┼─────────┼───────────┤
│ 3.10     │  26.29% │    76,580 │
│ 3.11     │  24.87% │    72,453 │
│ null     │  22.76% │    66,299 │
│ 3.9      │  20.74% │    60,426 │
│ 3.8      │   3.44% │    10,029 │
│ 3.7      │   1.19% │     3,469 │
│ 3.12     │   0.70% │     2,040 │
│ 3.6      │   0.01% │        32 │
│ 3.3      │   0.01% │        16 │
│ Total    │         │   291,344 │
└──────────┴─────────┴───────────┘

Date range: 2023-06-02 - 2023-11-29

We're currently unable to update these dependencies internally until we drop support for 3.7:

• coverage
• pytest-mock