[in-proc] Pin Microsoft.Extensions.DependencyModel to 6.x/8.x

[jviau]

Issue describing the changes in this PR

resolves #10660

Pull request checklist

IMPORTANT: Currently, changes must be backported to the in-proc branch to be included in Core Tools and non-Flex deployments.

• Backporting to the in-proc branch is not required
  • Otherwise: Link to backporting PR (this PR)
• 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
• My changes do not require diagnostic events changes
  • Otherwise: I have added/updated all related diagnostic events and their documentation (Documentation issue linked to PR)
• I have added all required tests (Unit tests, E2E tests)

Additional information

We aim to keep Microsoft.Extensions dependencies on the same major version train as the TFM - so 6.x to net6.0 and 8.x for net8.0. This PR addresses an assembly which was not following that, where it was previously resolved as 2.1

TODO

• verify API changes between 2.1 and 6.x/8.x
  • Went through, does not look like any breaking changes