add coverity workflow

Author: Didier Botella

.github/workflows/coverity.yaml

@@ -24,7 +24,8 @@ jobs:
       - name: Run a script
         run: |
           AUTH_KEY=${{ secrets.AUTH_KEY }}
-          bash ./get-auth.sh
+          echo ${{ secrets.AUTH_KEY }} > "./auth-key.txt"
+          chmod 400 auth-key.txt
         shell: bash
 
       - name: Coverity Full Scan