test: exclude 'not env.METACOV' more forcefully

Author: nedbat

metacov.ini

@@ -55,7 +55,7 @@ exclude_lines =
 
     # Lines that we can't run during metacov.
     pytest.mark.skipif\(env.METACOV
-    if not env.METACOV:
+    if (.* and)? not env.METACOV:
 
     # These lines only happen if tests fail.
     raise AssertionError