ci: skip integration tests completely for all PRs

[ZhongpinWang]

Currently, the integration tests (which are actually hundreds of e2e tests) are running for hours and triggered by each commit in any PRs.

Disabling it and only run it on the main branch.

Later on we should consider refactor e2e tests and leveraging the new sample code package.

[mwien]

To be precise, only the integration tests for gen take hours, the others take minutes. Also only the ones for gen currently fail currently as far as I can tell. So that's an argument for only disabling gen for now.

[ZhongpinWang]

To be precise, only the integration tests for gen take hours, the others take minutes. Also only the ones for gen currently fail currently as far as I can tell. So that's an argument for only disabling gen for now.

Yes your are right. I was only thinking if all tests should be sent to the remote server over network without having any mock server. Many integration tests also just check the shape of the response. Once we adopt the generation approach, even this won't be necessary. So we can keep them for now and I added base and core back. But in long term there are much room for improvement.