check-cabal-files.sh: exclude asserts.cabal

This suddenly started failing on CI even though this file has been there for
several weeks already 🤔

scripts/ci/check-cabal-files.sh

@@ -1,6 +1,6 @@
 #!/usr/bin/env bash
 
-for x in $(find . -name '*.cabal' | grep -v dist-newstyle | cut -c 3-); do
+for x in $(find . -name '*.cabal' | grep -vE 'dist-newstyle|asserts\.cabal' | cut -c 3-); do
   (
     d=$(dirname $x)
     echo "== $d =="