Draft: Fix flaky test Ci::Partitions::CreateService

Ref: #461272 (closed)

I was not able to reproduce this error locally so this is an attempt to fix this flaky spec.

What does this MR do and why?

This MR tries to fix a flaky test introduced in !152047 (merged).

According to our documentation we should use let_it_be_with_reload when testing changes to the given object as object defined with a let_it_be are considered as immutable.

# If you need to expect changes to the object in the test
let_it_be_with_reload(:project) { create(:project) }