GIT: test agg backend for matplotlib workflows.

Author: phmbressan

.github/workflows/test-pytest-slow.yaml

@@ -5,7 +5,7 @@ on:
     - cron: "0 17 * * 5"  # at 05:00 PM, only on Friday
   push:
     branches:
-      - main
+      - master
     paths:
       - "**.py"
       - ".github/**"
@@ -24,6 +24,7 @@ jobs:
         python-version: [3.9, 3.13]
     env:
       PYTHON: ${{ matrix.python-version }}
+      MPLBACKEND: Agg
     steps:
       - uses: actions/checkout@main
       - name: Set up Python

.github/workflows/test_pytest.yaml

@@ -23,6 +23,7 @@ jobs:
     env:
       OS: ${{ matrix.os }}
       PYTHON: ${{ matrix.python-version }}
+      MPLBACKEND: Agg
     steps:
       - uses: actions/checkout@main
       - name: Set up Python

rocketpy/rocket/aero_surface/air_brakes.py

@@ -207,8 +207,7 @@ def all_info(self):
         self.info()
         self.plots.drag_coefficient_curve()
 
-    # pylint: disable=unused-argument
-    def to_dict(self, **kwargs):
+    def to_dict(self, **kwargs):  # pylint: disable=unused-argument
         return {
             "drag_coefficient_curve": self.drag_coefficient,
             "reference_area": self.reference_area,