Fix resource manager: Add condition for opened PRs from dependabot (#19311)

Prevent dupe comments shipit when depedendabot PRs created.

## Description

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## Example Usage

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## Checklist

- [x] I have read and adhere to the [contribution
guide](https://github.com/Azure/bicep/blob/main/CONTRIBUTING.md).

###### Microsoft Reviewers: [Open in
CodeFlow](https://microsoft.github.io/open-pr/?codeflow=https://github.com/Azure/bicep/pull/19311)

Author: DragosDanielBoia

.github/policies/prMgmt.dependabot.yml

@@ -11,6 +11,8 @@ configuration:
       - description: Approve PRs submitted by dependabot with the "dependencies" label
         if:
           - payloadType: Pull_Request
+          - isAction:
+              action: Opened
           - hasLabel:
               label: dependencies
           - isActivitySender: