Add integration test for Fork Project Form Submission
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The following discussion from !53544 should be addressed:
- [ ] @vitallium started a [discussion](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/53544#note_520037300): (+1 comment)
> **suggestion (non-blocking):** Since these tests validate the behavior do you think we can move them to feature tests too? I am fine with leaving them here but IMO they look like integration tests.
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Please also see comment to test "Actual Forking" use case > https://gitlab.com/gitlab-org/gitlab/-/merge_requests/55461#note_520726904
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