Fix entrypoint.sh check available database

When using an external database, it cannot pass verification aviably

Fix entrypoint.sh check available database backend/testy/scripts/entrypoint.sh

- while ! nc -z db 5432; do
+ while ! nc -z $POSTGRES_SERVICE_HOST $POSTGRES_SERVICE_PORT; do

https://git.wikkeo.com/OPS/public-forks/yadro-testy/-/commit/c1efdd40286eded9523a3266e9dda55075b47a59