Fix LastExitCode handling in the shell integration pwsh sample

[mdgrs-mei]

The pwsh example for the shell integration does not report an error code once $LastExitCode is set to 0.

Try:

PS > cmd /c exit 0
PS > a

This PR fixes this issue by detecting external command errors using the history and the $Error variable.

[learn-build-service-prod[bot]]

Learn Build status updates of commit f715109:

:white_check_mark: Validation status: passed

File	Status	Preview URL	Details
TerminalDocs/tutorials/shell-integration.md	:white_check_mark:Succeeded	View

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