[flakiness] Correct group for TestEndpointAgentServiceMonitoring

[pkoutsovasilis]

What does this PR do?

This PR relocates TestEndpointAgentServiceMonitoring to the FleetEndpointSecurity execution group to prevent test failures caused by concurrent installation attempts of the Endpoint package when tests run in different groups.

Why is it important?

Reduces flakiness of Endpoint related tests that run in our CI

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

Disruptive User Impact

How to test this PR locally

Related issues

• Relates [Flaky Test]: TestForceInstallOverProtectedPolicy – Policy Response was: {{ 0 false [] { } }} #6969

[elastic-sonarqube]

Quality Gate passed

Issues
0 New issues
0 Fixed issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
0.0% Duplication on New Code

See analysis details on SonarQube

[elasticmachine]

⏳ Build in-progress, with failures

• Buildkite Build
• Commit: 8f13892

Failed CI Steps

• Win2022:sudo:default
• x86_64:sudo: fleet-endpoint-security
• x86_64:sudo: fleet-endpoint-security

cc @pkoutsovasilis