Fix documentation build in CI

CI is failing with

WARNING: The wheel package is not available.
WARNING: The wheel package is not available.
/home/runner/work/fmu-tools/fmu-tools/.eggs/setuptools_scm-8.0.4-py3.8.egg/setuptools_scm/_integration/setuptools.py:30: RuntimeWarning: 
ERROR: setuptools==56.0.0 is used in combination with setuptools_scm>=8.x

Your build configuration is incomplete and previously worked by accident!
setuptools_scm requires setuptools>=61

Suggested workaround if applicable:
 - migrating from the deprecated setup_requires mechanism to pep517/518
   and using a pyproject.toml to declare build dependencies
   which are reliably pre-installed before running the build tools

  warnings.warn(
WARNING setuptools_scm._integration.setuptools pyproject.toml does not contain a tool.setuptools_scm section
WARNING setuptools_scm.pyproject_reading toml section missing 'pyproject.toml does not contain a tool.setuptools_scm section'
usage: setup.py [global_opts] cmd1 [cmd1_opts] [cmd2 [cmd2_opts] ...]
   or: setup.py --help [cmd1 cmd2 ...]
   or: setup.py --help-commands
   or: setup.py cmd --help

error: invalid command 'build_sphinx'

There are a few things we could address here, but

https://github.com/equinor/fmu-tools/blob/e68c7059f2f1bd55649a446fdd1e2b2869921116/.github/workflows/fmu-tools.yml#L83

just needs to be swapped for the standard sphinx-build -b html docs build/docs/html command.

equinor / fmu-tools

Fix documentation build in CI #192