use DB_PORT for mysql database connection (#3762)

DB_PORT is the env variable defined for the mysql port into Panel Configuration.

.github/docker/entrypoint.sh

@@ -57,7 +57,7 @@ fi
 
 ## check for DB up before starting the panel
 echo "Checking database status."
-until nc -z -v -w30 $DB_HOST 3306
+until nc -z -v -w30 $DB_HOST $DB_PORT
 do
   echo "Waiting for database connection..."
   # wait for 1 seconds before check again