Fix the pinned build-system version

[kurtmckee]

Describe the changes

setuptools v45.x doesn't support pyproject.toml files.
v62.1.x and higher do, and continue to support Python 3.7.

Reproducer:

# Create a venv
python -m venv venv-demo
source venv-demo/bin/activate

# Install setuptools and build
python -m pip install setuptools==45.0.0 build

# Build the package using the already-installed setuptools
python -m build --no-isolation

This results in the following error:

ERROR Backend 'setuptools.build_meta' is not available.

Changing the reproducer to use setuptools 61.2.0 demonstrates that the issue is resolved.

Tasks

• Unit tests added that reproduce the issue or prove feature is working
• Fix or feature added
• Entry to release notes added
• Pre-commit CI shows no errors
• Unit tests passing
• For documentation changes: The Read the Docs preview builds and looks as expected

[mrbean-bremen]

Thanks, this looks sensible, as far as I can see!

I'm traveling right now, will have a closer look / merge next week when I have access to a computer.