Fix epic creation in LLM specs

What does this MR do and why?

Epic state_id enum declaration has been removed so we must use the integer value.

See !141954 (merged)

Example failure: https://gitlab.com/gitlab-org/gitlab/-/jobs/6002324186

You can test locally with:

bin/rspec /ee/spec/lib/gitlab/llm/chain/agents/zero_shot/qa_evaluation_spec.rb

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

assigned to @engwan

added devopsplan groupproject management maintenancepipelines typemaintenance labels

added sectiondev label

changed milestone to %16.9

changed the description

added backend label

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Category	Reviewer	Maintainer
backend	@atiwari71 (UTC+5.5, 2.5 hours behind author)	@alejandro (UTC-5, 13 hours behind author)

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Generated by Danger

@bcardoso- can you review please?

requested review from @bcardoso-

approved this merge request

@bcardoso-, thanks for approving this merge request.

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added pipeline:mr-approved label

requested review from @alejandro

removed review request for @bcardoso-

resolved all threads

enabled an automatic merge when all merge checks for 8aba9f6c pass

approved this merge request

mentioned in merge request !141816 (merged)

merged

mentioned in commit f94e3db8

added workflowstaging-canary label

added Category:Team Planning label

added workflowcanary label and removed workflowstaging-canary label

added workflowstaging label and removed workflowcanary label

added workflowproduction label and removed workflowstaging label

added workflowpost-deploy-db-staging label and removed workflowproduction label

added workflowpost-deploy-db-production label and removed workflowpost-deploy-db-staging label

added releasedcandidate label