[Az.SignalR] Update generation tool version: autorest.powershell v3->v4

[lijinpei2008]

Description

In 2026-05 release.

Mandatory Checklist

• Please choose the target release of Azure PowerShell. (⚠️Target release is a different concept from API readiness. Please click below links for details.)

  • [ ] General release
  • [ ] Public preview
  • [ ] Private preview
  • [ ] Engineering build
  • [ ] No need for a release

• [ ] Check this box to confirm: I have read the Submitting Changes section of CONTRIBUTING.md and reviewed the following information:

• SHOULD update ChangeLog.md file(s) appropriately
  • Update src/{{SERVICE}}/{{SERVICE}}/ChangeLog.md.
    • A snippet outlining the change(s) made in the PR should be written under the ## Upcoming Release header in the past tense.
  • Should not change ChangeLog.md if no new release is required, such as fixing test case only.
• SHOULD regenerate markdown help files if there is cmdlet API change. Instruction
• SHOULD have proper test coverage for changes in pull request.
• SHOULD NOT adjust version of module manually in pull request

[azure-client-tools-bot-prd[bot]]

Thanks for your contribution! The pull request validation has started. Please revisit this comment for updated status.

[github-actions[bot]]

‼️ DO NOT MERGE THIS PR ‼️ This PR was labeled "Do Not Merge" because it contains code change that cannot be merged. Please contact the reviewer for more information.