Fix CI: environment variable BRANCH is missed (#2111)

Signed-off-by: Yi Chen <[email protected]>
(cherry picked from commit e2693f1)

.github/workflows/integration.yaml

@@ -130,6 +130,8 @@ jobs:
 
       - name: Run chart-testing (lint)
         if: steps.list-changed.outputs.changed == 'true'
+        env:
+            BRANCH: ${{ steps.get_branch.outputs.BRANCH }}
         run: ct lint --check-version-increment=false --target-branch $BRANCH
 
       - name: Detect CRDs drift between chart and manifest