Consider using GitHub Actions as a primary CI

With the release of GitHub Actions CI/CD, it works perfectly fine with Testcontainers and can be used to run our tests.

Since we're working on migrating off Travis as our primary CI (see #1720), we need to consider which service to use instead, and GHA (GitHub Actions) looks like a good choice. It looks like Azure Pipelines (and AFAIK uses it under the hood) but does not come with Enterprise-style UI and users management, which is IMO better for an OSS project.

However, there are a few things in AZP (Azure Pipelines) that we still benefit from (listing them as checkboxes so that we can check them once there is such feature in GHA):

• self-hosted agents - we run our own agent for Docker for Windows CI due to licensing issues of Docker for Windows
• test result aggregation - sounds small, but this dramatically reduces the time it takes to figure out why the build is failing and also helped us to pinpoint a few flaky tests

Beginne mit der Prüfung des bestehenden Travis- und Azure-Pipelines-Setups sowie des Migrationskontexts in Issue #1720. Ermittle, ob GitHub Actions die erforderlichen selbst gehosteten Docker for Windows-Agents und die Aggregation von Testergebnissen bereitstellen kann; abgeschlossen ist die Aufgabe, wenn die primäre CI-Migration die benötigten Fähigkeiten erhält.