[CI] Run integration tests on EngFlow

[jpsim]

In #1995 I disabled remote execution for the integration test CI jobs because of test failures that were only occurring when using remote execution but ran fine on GitHub Actions workers directly.

Here's the kind of failure we were seeing when running these tests with remote execution: https://github.com/envoyproxy/envoy-mobile/runs/4739746396?check_suite_focus=true

And the same tests running successfully without remote execution: https://github.com/envoyproxy/envoy-mobile/runs/4740616118?check_suite_focus=true

[lfpino]

We have an easy fix for this one. @WillEngFlow will send you a PR in a bit.

[jpsim]

The tests in test/common/integration/BUILD were re-enabled on EngFlow in #2022, but the tests in test/swift/integration/BUILD still have no-remote-exec so I'm reopening this ticket to track that.

[lfpino]

This will be fixed with #2071