Excluded class macros from coverage.

I'm having problems on bullseye (Python 3.8).
Ideally only the decorator line should be excluded.

.coveragerc

@@ -7,5 +7,7 @@ omit = */kiplot/docopt.py
 [report]
 exclude_lines =
     pragma: no cover
+    @pre_class
+    @output_class
 #    raise RuntimeError