SPSite: Fix: SPSite Constructur returns $null when run as Ressource on SPSE

[ChristophHannappel]

Pull Request (PR) description

The Get Method failed to get an existing Site Collection on SharePoint Server Subscription Edition

This Pull Request (PR) fixes the following issues

• Fixes SPSite: Microsoft.SharePoint.SPSite Constructur returns $null when run as Ressource #1442

Task list

• Added an entry to the change log under the Unreleased section of the file CHANGELOG.md.
  Entry should say what was changed and how that affects users (if applicable), and
  reference the issue being resolved (if applicable).
• Resource documentation added/updated in README.md.
• Resource parameter descriptions added/updated in README.md, schema.mof and comment-based
  help.
• Comment-based help added/updated.
• Localization strings added/updated in all localization files as appropriate.
• Examples appropriately added/updated.
• Unit tests added/updated. See DSC Community Testing Guidelines.
• Integration tests added/updated (where possible). See DSC Community Testing Guidelines.
• New/changed code adheres to DSC Community Style Guidelines.

---

This change is 

[ykuijs]

The unit tests are failing for SPSE. Can you please fix those, so this PR can be merged and I can release a new version with both your fixes?