Fix build problem under Linux/macOS

[chenlei-yang]

Description

Fix issue #12456. Under Linux and macOS, when deleting PowerShell runtime files, one command contains $_.FullName, but for some reason that $_ didn't be recognized. A method to fix this is to add {} to involve $_.

Checklist

• I have read the Submitting Changes section of CONTRIBUTING.md
• The title of the PR is clear and informative
• 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
• The PR does not introduce breaking changes
• If applicable, the changes made in the PR have proper test coverage
• For public API changes to cmdlets:
  • a cmdlet design review was approved for the changes in this repository (Microsoft internal only)
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