[15.0][FIX] purchase_request_analytic: fill analytic account id in the purchase request

[AaronHForgeFlow]

When all the purchase request lines has the same analytic account the purchase request analytic account has to be the same.

This change fills analytic account id in the purchase request when all the lines have same analytic account id.

Before this change the analytic account is empty in those cases, and because of that, the search of purchase request by analytic account is not working

cc @ForgeFlow

[AaronHForgeFlow]

@ps-tubtim is this ok to you?

[StefanRijnhart]

Would it be possible to add a small test?

[AaronHForgeFlow]

@StefanRijnhart small tests added :) sorry for the diff, took the opportunity to rename a variable name

[OCA-git-bot]

This PR has the approved label and has been created more than 5 days ago. It should therefore be ready to merge by a maintainer (or a PSC member if the concerned addon has no declared maintainer). 🤖

[StefanRijnhart]

/ocabot merge patch

[OCA-git-bot]

Hey, thanks for contributing! Proceeding to merge this for you. Prepared branch 15.0-ocabot-merge-pr-636-by-StefanRijnhart-bump-patch, awaiting test results.

[OCA-git-bot]

Congratulations, your PR was merged at d6fe93f00bf22ce2677d3d54ec2824bbba2bce5c. Thanks a lot for contributing to OCA. ❤️