fix: do not add trailing commit the last positional parameter already…

[a-wallen]

… has one

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[copybara-service]

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[a-wallen]

https://critique.corp.google.com/cl/695463353

[copybara-service]

https://dart-review.googlesource.com/c/sdk/+/394660 has been updated with the latest commits from this pull request.

[copybara-service]

https://dart-review.googlesource.com/c/sdk/+/394660 has been updated with the latest commits from this pull request.

[bwilkerson]

In case it wasn't clear to you, the review is happening at https://dart-review.googlesource.com/c/sdk/+/394660. You'll need to use that link to open Garret so that you can read the review comments. You can reply to comments there, but you can also make changes and push new commits to the PR the way you would for any GitHub review and they will be copied to Garret.