Fix: Wrong python syntax for report warnings

The syntax must have changed a while ago, but nobody noticed so far.
`self.report({'WARN'}..` no longer works. Replaced with 'WARNING'

Pull Request: https://projects.blender.org/blender/blender/pulls/148110

scripts/startup/bl_operators/anim.py

@@ -114,7 +114,7 @@ class ANIM_OT_keying_set_export(Operator):
 
                 if not found:
                     self.report(
-                        {'WARN'},
+                        {'WARNING'},
                         rpt_("Could not find material or light using Shader Node Tree - {:s}").format(str(ksp.id)),
                     )
             elif ksp.id.bl_rna.identifier.startswith("CompositorNodeTree"):
@@ -126,7 +126,7 @@ class ANIM_OT_keying_set_export(Operator):
                         break
                 else:
                     self.report(
-                        {'WARN'},
+                        {'WARNING'},
                         rpt_("Could not find scene using Compositor Node Tree - {:s}").format(str(ksp.id)),
                     )
             elif ksp.id.bl_rna.name == "Key":