Support environment markers in requires fields (#12711)

stubs/seaborn/METADATA.toml

@@ -2,7 +2,15 @@ version = "0.13.2"
 # Requires a version of numpy and matplotlib with a `py.typed` file
 # see https://github.com/python/typeshed/issues/12551
 # on why we need the upper bound for numpy
-requires = ["matplotlib>=3.8", "numpy>=1.20,<2.1.0", "pandas-stubs"]
+#
+# TODO: Specifying the python-version for matplotlib should not be necessary,
+# because of the requires_python field. However, this needs changes to
+# get_typeshed_stub_version.py (see there).
+requires = [
+    "matplotlib>=3.8; python_version>='3.9'",
+    "numpy>=1.20,<2.1.0",
+    "pandas-stubs",
+]
 # matplotlib>=3.8 requires Python >=3.9
 requires_python = ">=3.9"
 upstream_repository = "https://github.com/mwaskom/seaborn"