Synapse 1.81.0 fails to build with poetry-core < 1.1.0 (despite lower bound of >= 1.0.0)

[DMRobertson]

Note that support for dependency groups was added in poetry core 1.1.0.

Poetry-core 1.0.8 rejects this syntax:

RuntimeError: The Poetry configuration is invalid:
  - Additional properties are not allowed ('group' was unexpected

which unfortunately means that the poetry-core range given in

synapse/pyproject.toml

Lines 365 to 372 in edf046e

	[build-system]
	# The upper bounds here are defensive, intended to prevent situations like
	# #13849 and #14079 where we see buildtime or runtime errors caused by build
	# system changes.
	# We are happy to raise these upper bounds upon request,
	# provided we check that it's safe to do so (i.e. that CI passes).
	requires = ["poetry-core>=1.0.0,<=1.5.0", "setuptools_rust>=1.3,<=1.5.2"]
	build-backend = "poetry.core.masonry.api"

can no longer build Synapse at the lower end of the version range.

Options:

• Move these into the tool.poetry.dev-dependencies section above, or
• Bump the lower bound to >=1.1.0 and liaise with packagers, or
• ??? something else?

Actions:

• We should probably ensure something in CI tries to build a wheel using the oldest supported version of poetry-core

Originally posted by @DMRobertson in #15265 (comment)