fix: right version for 8.0

[mdelapenya]

What does this PR do?

It updates the version of the elastic-agent on its Docker Compose.

Why is it important?

Keep versions up-to-date

Checklist

• 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 run the Unit tests (make unit-test), and they are passing locally
• I have run the End-2-End tests for the suite I'm working on, and they are passing locally
• I have noticed new Go dependencies (run make notice in the proper directory)

[elasticmachine]

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[mdelapenya]

Stack not starting, but fixed in #2133