sync warning settings

_CoqProject

 -Q theories refinedc
 # 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.
+# Cannot use non-canonical projections as it causes massive unification failures
+# (https://github.com/coq/coq/issues/6294).
 -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