silence another warning

_CoqProject

@@ -9,6 +9,8 @@
 -arg -w -arg -argument-scope-delimiter
 # Fixing this requires Coq 8.20.
 -arg -w -arg -deprecated-since-8.20
+# https://gitlab.mpi-sws.org/iris/stdpp/-/issues/216
+-arg -w -arg -notation-incompatible-prefix
 
 stdpp/options.v
 stdpp/base.v