sel4-deps: cython >=3 breaks pyyaml < 5.4 at build

Require cython < 3, because >=3 breaks the install for pyyaml < 5.4 at
build/install time for more recent python version.

pyyaml 5.4 also breaks, but is not fixed by downgrading cython, so we
also require pyyaml < 5.4.

See also <https://github.com/yaml/pyyaml/issues/601>

Signed-off-by: Gerwin Klein <gerwin.klein@proofcraft.systems>

tools/python-deps/setup.py

@@ -35,7 +35,8 @@ DEPS = [
     'pyelftools',
     'sh',
     'pexpect',
-    'pyyaml>=5.1,<6',
+    'cython<3',  # build dependency for pyyaml 5; see https://github.com/yaml/pyyaml/issues/601
+    'pyyaml>=5.1,<5.4',  # <5.4 for cmake-format==0.4.5
     'jsonschema',
     'pyfdt',
     'cmake-format==0.4.5',