Docker-in-docker inside GitHub Actions, can't access Container from within Container

Question

I'm running my CI from within a docker container with docker installed. Inside that docker container, I'm running docker-compose with a postgres database. Even though the postgres database has fully started, I can't access it at localhost:8090, like I should be able to.

I'm using the container syntax to run my github actions in a container. (tilt is running docker-compose for me) i.e.:

  build-tilt:
    name: Build Tilt
    runs-on: [ self-hosted, docker ]
    container:
      image: devitllc/coretto-build:17

    steps:
      - name: Checkout code
        uses: actions/checkout@v3

      - name: Tilt CI
        run: tilt ci --timeout 15m --debug

docker-compose.yml:

version: "3.9"
services:

  postgres:
    image: postgres:14
    ports:
      - "8090:5432"
    environment:
      POSTGRES_USER: postgres
      POSTGRES_PASSWORD: test
      POSTGRES_DB: example
    volumes:
      - example-postgres:/var/lib/postgresql/data
    deploy:
      resources:
        limits:
          memory: 1g
    healthcheck:
      test: CMD pg_isready -U postgres
      interval: 5s
      timeout: 5s
      retries: 10

I've tried accessing it at postgres as well, and I'm unsure what I'm doing wrong. Perhaps I need to do something with networks? I don't have enough docker experience with networks to know what I should be doing.

I'm running multiple github actions runners from a single computer, so ideally nothing would be exposed outside of the container I'm using to run my container in.

EDIT: An example reproducing the failure, is here: https://github.com/ScottPierce/DockerInDockerNetworkingError

The CI logs are here: https://github.com/ScottPierce/DockerInDockerNetworkingError/actions Notice that it succeeds when it's not docker-in-docker.