build: manually add matplotlib dep

pyproject.toml

@@ -14,6 +14,7 @@ networkx = "~3.2.0"         # max available version with python 3.9 support
 jsonpointer = "^3.0.0"
 types-networkx = "~3.2.1.20240918"
 datamodel-code-generator = "^0.26.3"
+matplotlib = "^3.9.4"
 
 
 [tool.poetry.group.test.dependencies]

qualibrate/qualibration_node.py

@@ -16,7 +16,10 @@
 )
 
 import matplotlib
-from matplotlib.rcsetup import interactive_bk
+from matplotlib.backends import (  # type: ignore[attr-defined]
+    BackendFilter,
+    backend_registry,
+)
 from pydantic import ValidationError, create_model
 
 from qualibrate.config.utils import get_qualibrate_app_settings
@@ -263,7 +266,10 @@ def _warn_if_external_and_interactive_mpl(self) -> None:
 
         """
         mpl_backend = matplotlib.get_backend()
-        if self.modes.external and mpl_backend in interactive_bk:
+        if self.modes.external and mpl_backend in cast(
+            list[str],
+            backend_registry.list_builtin(BackendFilter.INTERACTIVE),  # type: ignore[no-untyped-call]
+        ):
             matplotlib.use("agg")
             logger.warning(
                 f"Using interactive matplotlib backend '{mpl_backend}' in "