MINOR: skip ci-complete on 4.0 (#20644)

Since that 4.0 branch does not include
[KAFKA-18748](https://issues.apache.org/jira/browse/KAFKA-18748), it is
unable to find the related scan reports, but the ci-complete workflow is
still being triggered on the 4.0 branch. Disable this on the 4.0 branch,
as its reports can be safely ignored.

See #20616 (comment).

Reviewers: Chia-Ping Tsai <[email protected]>

Author: Yunyung

.github/workflows/ci-complete.yml

@@ -38,7 +38,7 @@ run-name: Build Scans for ${{ github.event.workflow_run.display_title}}
 jobs:
   upload-build-scan:
     # Skip this workflow if the CI run was skipped or cancelled
-    if: (github.event.workflow_run.conclusion == 'success' || github.event.workflow_run.conclusion == 'failure')
+    if: (github.event.workflow_run.conclusion == 'success' || github.event.workflow_run.conclusion == 'failure') && github.event.workflow_run.head_branch != '4.0'
     runs-on: ubuntu-latest
     strategy:
       fail-fast: false