Force Agg backend before patchworklib import to fix Windows CI tkinter error

Author: tmsincomb

src/tpixel/renderer.py

@@ -113,6 +113,7 @@ def to_patchwork(panel: Panel, label: str = "tpixel") -> "pw.Brick":
     Returns:
         A ``patchworklib.Brick`` ready for composition.
     """
+    matplotlib.use("Agg")
     import patchworklib as pw
 
     w, h = panel_figsize(panel)

tests/test_patchwork.py

@@ -2,8 +2,11 @@
 
 from __future__ import annotations
 
-import matplotlib.pyplot as plt
-import patchworklib as pw
+import matplotlib
+matplotlib.use("Agg")
+
+import matplotlib.pyplot as plt  # noqa: E402
+import patchworklib as pw  # noqa: E402
 
 from tpixel.models import Marker, Panel, Region, SeqGroup
 from tpixel.renderer import panel_figsize, plot_panel, to_patchwork