stay on latest Cython 0.29 (0.29.36) for borg 1.2.x

master branch tests Cython 3 now.
1.2-maint branch may or may not upgrade to build with Cython 3 later.

pyproject.toml

@@ -1,3 +1,3 @@
 [build-system]
-requires = ["setuptools", "pkgconfig", "Cython", "setuptools_scm>=1.7"]
+requires = ["setuptools", "pkgconfig", "Cython<3", "setuptools_scm>=1.7"]
 build-backend = "setuptools.build_meta"

requirements.d/development.lock.txt

@@ -8,6 +8,6 @@ pytest==7.2.0
 pytest-xdist==3.1.0
 pytest-cov==4.0.0
 pytest-benchmark==4.0.0
-Cython==0.29.33
+Cython==0.29.36
 twine==4.0.2
 python-dateutil==2.8.2