fix(workflow): downgrade test-upgrade-legacy version to 2021.7.9

- Changed the `version` in the test-upgrade-legacy workflow from 2023.7.0 to 2021.7.9.
- Ensured compatibility with older versions for testing purposes.

.github/workflows/test-upgrade-legacy.yaml

@@ -42,7 +42,7 @@ jobs:
       matrix:
         architecture: [large-with-two-compilers]
         image: [almalinux-cloud/almalinux-8]
-        version: [2023.7.0]
+        version: [2021.7.9]
         to_version: [2023.8.0]
     steps:
       - name: Start SSH session