ci(helm): update Kube Diff workflow (#14173)

Signed-off-by: Vladyslav Diachenko <vlad.diachenko@grafana.com>

.github/workflows/helm-loki-ci.yml

@@ -32,12 +32,14 @@ jobs:
         uses: actions/checkout@v4
         with:
           ref: ${{ github.event.pull_request.base.ref }}
+          repository: ${{ github.event.pull_request.base.repo.full_name }}
           path: ${{ github.workspace }}/base
 
       - name: Checkout PR branch to 'pr' folder within workspace
         uses: actions/checkout@v4
         with:
           ref: ${{ github.event.pull_request.head.ref }}
+          repository: ${{ github.event.pull_request.head.repo.full_name }}
           path: ${{ github.workspace }}/pr
 
       - name: Render Helm chart for each scenario in the base branch