Update Set-AzApiManagementGroup.md because of missing required parameter in example

[erwinkramer]

GroupId is a required parameter, please add this in the example as well.

Description

Checklist

• [x ] I have read the Submitting Changes section of CONTRIBUTING.md
• [x ] The title of the PR is clear and informative
• [your job ] The appropriate ChangeLog.md file(s) has been updated:
  • For any service, the ChangeLog.md file can be found at src/{{SERVICE}}/{{SERVICE}}/ChangeLog.md
  • A snippet outlining the change(s) made in the PR should be written under the ## Upcoming Release header -- no new version header should be added
• [x ] The PR does not introduce breaking changes
• [x ] If applicable, the changes made in the PR have proper test coverage
• [x ] For public API changes to cmdlets:
  • [x ] a cmdlet design review was approved for the changes in this repository (Microsoft internal only)
  • [x ] the markdown help files have been regenerated using the commands listed here

[adxsdkps]

Can one of the admins verify this patch?

[msJinLei]

@erwinkramer Please also add your modification explanation into the Changlog.md under ApiManagement folder, thanks.

[msftclas]

All CLA requirements met.

[erwinkramer]

@msJinLei i've updated the changelog accordingly.

[msJinLei]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 3 pipeline(s).

[msJinLei]

@msJinLei i've updated the changelog accordingly.

@erwinkramer, the changelog should be added under upcoming release. Please refer to my commit in your branch. You can follow that rule next time.