[ci] Fix bug involved by PR 11810 which affect official build pipeline (

sonic-net#11891)

Why I did it
Fix the official build not triggered correctly issue, caused by the azp template path not existing.

How I did it
Change the azp template path.

.azure-pipelines/official-build.yml

@@ -38,7 +38,7 @@ stages:
   variables:
   - name: CACHE_MODE
     value: wcache
-  - template: azure-pipelines-repd-build-variables.yml@buildimage
+  - template: .azure-pipelines/azure-pipelines-repd-build-variables.yml@buildimage
   jobs:
   - template: azure-pipelines-build.yml
     parameters: