Fix artifact path in plugin deployment workflow (#449)

### Motivation and Context

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Incorrect artifact path in the plugin deployment workflow is causing the
deployment to fail.

### Description

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Fix the path.

### Contribution Checklist

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- [ ] The code builds clean without any errors or warnings
- [ ] The PR follows the [Contribution
Guidelines](https://github.com/microsoft/chat-copilot/blob/main/CONTRIBUTING.md)
and the [pre-submission formatting
script](https://github.com/microsoft/chat-copilot/blob/main/CONTRIBUTING.md#development-scripts)
raises no violations
- [ ] All unit tests pass, and I have added new tests where possible
- [ ] I didn't break anyone 😄

.github/workflows/copilot-deploy-plugins.yml

@@ -68,4 +68,4 @@ jobs:
             --deployment-name ${{inputs.DEPLOYMENT_NAME}} \
             --subscription ${{secrets.AZURE_SUBSCRIPTION_ID}} \
             --resource-group ${{vars.CC_DEPLOYMENT_GROUP_NAME}} \
-            --packages "${{ github.workspace }}/${{inputs.ARTIFACT_NAME}}/plugins"
+            --packages "${{ github.workspace }}/${{inputs.ARTIFACT_NAME}}"