ci: include scripts/find-banned.sh

...to search for functions which have been banned from our code base,
because they're too easy to misuse, and even if used correctly,
complicate audits, cause inconsistencies and/or make static analysis
harder.

.github/workflows/build.yml

@@ -18,6 +18,8 @@ jobs:
       - name: Code Style
         run: |
           ./scripts/check
+          make -C scripts/helper
+          ./scripts/find-banned.sh
   build:
     name: Build
     needs: codestyle

scripts/helper/.gitignore

@@ -0,0 +1,2 @@
+find-idents
+*.o