fix: Set github user in nightly release pipeline (#24850)

* fix: Set github user in nightly release pipeline

* use rm -f

azure-pipelines.release-vnext-nightly.yml

@@ -37,14 +37,19 @@ jobs:
     steps:
       - template: .devops/templates/tools.yml
 
+      - script: |
+          git config user.name "Fluent UI Build"
+          git config user.email "[email protected]"
+        displayName: Configure git user (used by beachball)
+
       - task: Bash@3
         inputs:
           filePath: yarn-ci.sh
         displayName: yarn
 
         # Deletes all existing changefiles so that only bump that happens is for nightly
       - script: |
-          rm change/*
+          rm -f change/*
         displayName: 'Delete existing changefiles'
 
         # Bumps all v9 packages to a x.x.x-nightly.commitSha version and checks in change files