GitHub Actions workflows were broken

[moreal]

Now, there are two broken workflows, on push, push docker image, and you can see the logs in there push docker image/build_and_push#152ecf5, on push/build#152ecf5.

The reasons for them are each below:

• The action, actions/gcloud, has deprecated since the new GitHub Actions workflow syntax, perhaps.
• In Dockerfile, it is based on mcr.microsoft.com/dotnet/core/sdk:2.2 yet, though #99 was applied.
  • IMO it was not caught because it doesn't check the docker image build in the pull-request step. Furthermore, IMHO it is enough to check build status with only docker image build.

To work:

• [x] We should use GoogleCloudPlatform/github-actions/setup-gcloud instead the deprecated action.
• [x] We should update Dockerfile to use mcr.microsoft.com/dotnet/core/sdk:3.1.
  • [ ] IMO I believe it will be better if the docker image build step is also available on the pull-request step.

[moreal]

We should update Dockerfile to use mcr.microsoft.com/dotnet/core/sdk:3.1.

It was resolved in #102

[moreal]

We should use GoogleCloudPlatform/github-actions/setup-gcloud instead the deprecated action.

It was resolved in #126.