Update Extension Validation Template

[satvu]

Issue describing the changes in this PR

resolves issue where release pipeline attempts to pack generated validation projects.

Pull request checklist

• My changes do not require documentation changes
  • Otherwise: Documentation issue linked to PR
• My changes should not be added to the release notes for the next release
  • Otherwise: I've added my notes to release_notes.md
• My changes do not need to be backported to a previous version
  • Otherwise: Backport tracked by issue/PR #issue_or_pr
• I have added all required tests (Unit tests, E2E tests)

[jviau]

Not sure if PR build runs pack. You may want to manually validate that.

[satvu]

Not sure if PR build runs pack. You may want to manually validate that.

Validated locally - no errors, no nuget package created.