Fix upmerge samples to edge workflow

[sk593]

Bug information

Steps to reproduce (required)

The upmerge samples to edge workflow fails when there's nothing to commit. This is okay since there were technically no changes but the workflow should still pass in this case

https://github.com/radius-project/samples/actions/workflows/upmerge.yaml

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Desired behavior (required)

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Additional context

AB#12892

[azure-boards]

✅ Successfully linked to Azure Boards work item(s):

• GitHub Issue 12892

[brooke-hamilton]

/assign @brooke-hamilton

[brooke-hamilton]

@sk593 is the desired behavior that the workflow should complete without creating a PR if there are no changes to commit?

[sk593]

@sk593 is the desired behavior that the workflow should complete without creating a PR if there are no changes to commit?

yup! the upmerge workflow should keep edge up to date with the current release branch. so if there are no changes, there's no need to create a PR