chore(tests): rename LTS_JENKINS_VERSION in bake tests

[lemeurherve]

This PR updates this variable name, forgot to transplant a4c0d57 when extracting #2184 from #2178.

Testing done

bats ./tests/bake.bats

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[lemeurherve]

As this PR has absolutely no behavior change, and to avoid running a build on CI for nothing, I'm force-squashing this PR.