[9.0](backport #7056) Disable interpolation for monorepo plugin

[mergify]

What does this PR do?

Set "interpolation" to false for buildkite monorepo plugin.

Why is it important?

It can cause error in pipelines when "buildkite upload command used.

Checklist

• I have read and understood the pull request guidelines of this project.
• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in ./changelog/fragments using the changelog tool
• I have added an integration test or an E2E test

Related issues

---

This is an automatic backport of pull request #7056 done by [Mergify](https://mergify.com).

[elasticmachine]

💔 Build Failed

• Buildkite Build
• Commit: a58d54d

Failed CI Steps

• Unit tests - Windows 2016

History

cc @ev1yehor

[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