[8.x](backport #5868) remove DEV=true from CI build steps

[mergify]

In CI we see failures like elastic/beats#41270

Removing DEV=true from CI builds should fix.

---

This is an automatic backport of pull request #5868 done by Mergify.

[mergify]

Cherry-pick of c9cd580 has failed:

On branch mergify/bp/8.x/pr-5868
Your branch is up to date with 'origin/8.x'.

You are currently cherry-picking commit c9cd580456.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   .buildkite/scripts/steps/integration-package.sh
	both modified:   .buildkite/scripts/steps/k8s-extended-tests.sh

no changes added to commit (use "git add" and/or "git commit -a")

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[elasticmachine]

Pinging @elastic/elastic-agent-data-plane (Team:Elastic-Agent-Data-Plane)

[elastic-sonarqube]

Quality Gate passed

Issues
0 New issues
0 Fixed issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
No data about Duplication

See analysis details on SonarQube