Pin Blender for CI asset processing (#58)

Reviewed-on: #58
Co-authored-by: Álex Román Núñez <eirexe@eirteam.moe>

src/blend_asset/export.py

@@ -7,6 +7,15 @@ import sys
 def main():
     output = sys.argv[sys.argv.index("--") + 1]
     actions_path = sys.argv[sys.argv.index("--") + 2]
+    source_path = sys.argv[sys.argv.index("--") + 3]
+    loaded_path = os.path.realpath(bpy.data.filepath)
+    expected_path = os.path.realpath(source_path)
+    if loaded_path != expected_path:
+        raise RuntimeError(
+            f"Blender loaded {loaded_path!r} instead of {expected_path!r}"
+        )
+    if not bpy.data.objects or not bpy.data.meshes:
+        raise RuntimeError("Blender loaded an empty scene")
     with open(actions_path) as file:
         actions_to_keep = set(json.load(file))