Dropping Python 3.7 support

[zanieb]

Python 3.7 has reached EOL and support is being dropped in the tooling required to maintain this repository e.g. black, pytest, support is likely to eventually be dropped in our runtime dependencies as well.

Since it is not easy to install an older version of ruff-lsp when using ruff-vscode, we'd like to retain 3.7 support for a bit longer.

We can pin developer tooling with little consequence. When runtime dependencies drop 3.7 support, we may need to investigate bundling multiple versions of the libraries to retain 3.7 support. If that is costly, we will need to choose between having outdated dependencies for all Python versions or dropping 3.7 support.

[zanieb]

Blocked upgrades:

• Bump zipp from 3.15.0 to 3.16.0 #183
• Bump python-lsp-jsonrpc from 1.0.0 to 1.1.0 #241
• Bump pip-tools from 6.14.0 to 7.0.0 #195
• Bump typeguard from 4.1.2 to 4.1.3 #224
• Bump pluggy from 1.2.0 to 1.3.0 #226
• Bump importlib-metadata from 6.7.0 to 6.8.0 #184
• Bump black from 23.3.0 to 23.7.0 #185
• Bump mypy from 1.4.1 to 1.5.0 #213
• Bump pytest-asyncio from 0.21.1 to 0.22.0 #304
• Bump cattrs from 23.1.2 to 23.2.1 #325
• Use macos-13 for CI #448 (Upgrade to macos-latest)