ci: set ignore-error to true to avoid gh rate limit error

[crazy-max]

alternative to https://github.com/moby/buildkit/pull/4702 closes #4702

Sets ignore-error=true in our workflows to avoid it to fail if we are hitting the rate limit but don't set it in our integration test: https://github.com/moby/buildkit/blob/03caf1a405a5b402a3d0b485d6b0e3092760191b/client/client_test.go#L5711-L5719