Remove isAction check for dependabot PRs (#19599)

Unfortunately this recent change means that PRs are no longer
auto-approved if dependabot pushes a 2nd update (e.g. to resolve merge
conflicts)
###### Microsoft Reviewers: [Open in
CodeFlow](https://microsoft.github.io/open-pr/?codeflow=https://github.com/Azure/bicep/pull/19599)

Author: anthony-c-martin

.github/policies/prMgmt.dependabot.yml

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