Change the tags names according to the curent state (#11059)

## Problem
We have not synced `force-test-extensions-upgrade.yml` with the last
changes.
The variable `TEST_EXTENSIONS_UPGRADE` was ignored in the script and
actually set to `NEW_COMPUTE_TAG` while it should be set to
`OLD_COMPUTE_TAG` as we are about to run compatibility tests.
## Summary of changes
The tag names were synced, the logic was fixed.

.github/workflows/force-test-extensions-upgrade.yml

@@ -52,8 +52,9 @@ jobs:
       - name: Test extension upgrade
         timeout-minutes: 20
         env:
-          NEWTAG: latest
-          OLDTAG: ${{ steps.get-last-compute-release-tag.outputs.tag }}
+          NEW_COMPUTE_TAG: latest
+          OLD_COMPUTE_TAG: ${{ steps.get-last-compute-release-tag.outputs.tag }}
+          TEST_EXTENSIONS_TAG: ${{ steps.get-last-compute-release-tag.outputs.tag }}
           PG_VERSION: ${{ matrix.pg-version }}
           FORCE_ALL_UPGRADE_TESTS: true
         run: ./docker-compose/test_extensions_upgrade.sh