Fix formatting for Set-ItResult with because, removing trailing comma and redundant "because"

[wethreetrees]

PR Summary

Fix #2588

Fixes the formatting of the Set-ItResult exception message when a -Because is provided.

This change removes the "because" being added to the message before including the content of Format-Because (which includes the "because"). It also strips out the trailing comma, as it's not needed or expected here.

The current message is formatted with a redundant "because" and a trailing comma.

ex:

try {
    Set-ItResult -Skipped -Because "we are forcing it to skip"
} catch {
    $_.Exception.Message
}

Expected:

is skipped, because we are forcing it to skip

Actual:

is skipped, because  because we are forcing it to skip,

PR Checklist

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• Tests are added/update (if required)
• Documentation is updated/added (if required)

[nohwnd]

/backport to 5.x.x

[github-actions]

Started backporting to 5.x.x: https://github.com/pester/Pester/actions/runs/12349993536

[github-actions]

@nohwnd an error occurred while backporting to 5.x.x, please check the run log for details!

The process '/usr/bin/git' failed with exit code 1

[nohwnd]

/backport to rel/5.x.x

[github-actions]

Started backporting to rel/5.x.x: https://github.com/pester/Pester/actions/runs/12389574371