Upper bound build-system requirements

pyproject.toml

@@ -307,7 +307,11 @@ twine = "*"
 towncrier = ">=18.6.0rc1"
 
 [build-system]
-requires = ["poetry-core>=1.0.0", "setuptools_rust>=1.3"]
+# 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,<=1.3.1", "setuptools_rust>=1.3,<=1.5.2"]
 build-backend = "poetry.core.masonry.api"