fix group site url ref in sanity yml (#4502)

#### Does this PR need a docs update or release note?

- [x] ⛔ No

#### Type of change

- [x] 🐛 Bugfix


#### Test Plan

- [x] 💚 E2E

.github/workflows/sanity-test.yaml

@@ -372,7 +372,7 @@ jobs:
         working-directory: ./src/cmd/factory
         run: |
           go run . sharepoint files  \
-            --site ${{ env.CORSO_M365_TEST_GROUPS_SITE_URL }} \
+            --site ${{ vars.CORSO_M365_TEST_GROUPS_SITE_URL }} \
             --user ${{ env.TEST_USER }} \
             --secondaryuser  ${{ env.CORSO_SECONDARY_M365_TEST_USER_ID }} \
             --tenant ${{ secrets.TENANT_ID }} \
@@ -385,7 +385,7 @@ jobs:
         with:
           service: groups
           kind: incremental
-          backup-args: '--site "${{ env.CORSO_M365_TEST_GROUPS_SITE_URL }}"'
+          backup-args: '--site "${{ vars.CORSO_M365_TEST_GROUPS_SITE_URL }}"'
           restore-args: '--folder ${{ env.RESTORE_DEST_PFX }}${{ steps.new-data-creation-groups.outputs.result }}'
           restore-container: '${{ env.RESTORE_DEST_PFX }}${{ steps.new-data-creation-groups.outputs.result }}'
           log-dir: ${{ env.CORSO_LOG_DIR }}