[CI] Test for server-side virtual thread support

[jrhee17]

Motivation:

Explain why you're making this change and what problem you're trying to solve.

Modifications:

• List the modifications you've made in detail.

Result:

• Closes #. (If this resolves the issue.)
• Describe the consequences that a user will face after this PR is merged.

[github-actions]

🔍 Build Scan® (commit: a9256be)

Job name	Status	Build Scan®
build-windows-latest-jdk-21	❌ (failure)	https://ge.armeria.dev/s/a2hpowgw2vlp2
build-self-hosted-unsafe-jdk-8	❌ (failure)	https://ge.armeria.dev/s/54gdshvit3k3s
build-self-hosted-unsafe-jdk-21-snapshot-blockhound	❌ (failure)	https://ge.armeria.dev/s/ibcvrq2cpjegs
build-self-hosted-unsafe-jdk-17-min-java-17-coverage	❌ (failure)	https://ge.armeria.dev/s/vdpcr2naaaooy
build-self-hosted-unsafe-jdk-17-min-java-11	❌ (failure)	https://ge.armeria.dev/s/pff5qxskrp4m4
build-self-hosted-unsafe-jdk-17-leak	❌ (failure)	https://ge.armeria.dev/s/pl5d6disixlfs
build-self-hosted-unsafe-jdk-11	❌ (failure)	https://ge.armeria.dev/s/u4azsl3vmcfxe
build-macos-12-jdk-21	❌ (failure)	https://ge.armeria.dev/s/kxyyty4gd3zpm