fix(c): don't use Cython 3.1 or following to build the extension

The resulting module seems affected by a memory leak.

https://github.com/cython/cython/issues/6850

diff --git a/psycopg_c/pyproject.toml b/psycopg_c/pyproject.toml
index 905dfd0ed2d57ece358f0c4001cb9a6afd77cbc1..cb332ec39a47ffbefcb3e263ff25dcd8ed87ab8d 100644 (file)
--- a/psycopg_c/pyproject.toml
+++ b/psycopg_c/pyproject.toml
@@ -19,7 +19,12 @@ backend-path = ["build_backend"]
 
 [cython-backend]
 # These packages are only installed if there are pyx files to compile.
-cython-requires = ["Cython >= 3.0.0"]
+
+# Don't install Cython 3.1: https://github.com/cython/cython/issues/6850
+# TODO: When the bug is solved we will remove the upper bound of the version
+# and just exclude the known broken versions, or we will establish a new
+# lower bound.
+cython-requires = ["Cython >= 3.0.0, < 3.1.0"]
 
 [project]
 name = "psycopg-c"