Update _CoqProject flags.

_CoqProject

 -Q theories iris_ora
--arg -w -arg -notation-overridden,-redundant-canonical-projection,-several-object-files
+# We sometimes want to locally override notation and there is no good way to do that with scopes.
+-arg -w -arg -notation-overridden
+# non-canonical projections (https://github.com/coq/coq/pull/10076) do not exist yet in 8.9.
+-arg -w -arg -redundant-canonical-projection
+# change_no_check does not exist yet in 8.9.
+-arg -w -arg -convert_concl_no_check
+# "Declare Scope" does not exist yet in 8.9.
+-arg -w -arg -undeclared-scope
+# We have ambiguous paths and so far it is not even clear what they are (https://gitlab.mpi-sws.org/iris/iris/issues/240).
+-arg -w -arg -ambiguous-paths
+
 theories/algebra/ora.v
 theories/algebra/osum.v
 theories/algebra/agree.v