fix tcl flakiness on windows runners

Author: wpbonelli

test/conftest.py

@@ -1,4 +1,8 @@
 from pathlib import Path
+from platform import system
+
+import pytest
+from modflow_devtools.misc import is_in_ci
 
 pytest_plugins = ["modflow_devtools.fixtures"]
 
@@ -8,6 +12,15 @@
 EXCLUDED_EXAMPLES = []
 
 
+@pytest.fixture(scope="session", autouse=True)
+def patch_macos_ci_matplotlib():
+    # use noninteractive matplotlib backend if in Mac OS CI to avoid pytest-xdist node failure
+    if is_in_ci() and system().lower() == "darwin":
+        import matplotlib
+
+        matplotlib.use("agg")
+
+
 def pytest_generate_tests(metafunc):
     if "example_script" in metafunc.fixturenames:
         scripts = {