fix: drop ubuntu:16.04 from scripted input tests (EOL) (#495)

### Description

drop ubuntu:16.04 from scripted input tests (EOL) 

### Checklist

- [ ] `README.md` has been updated or is not required
- [ ] push trigger tests
- [ ] manual release test
- [ ] automated releases test
- [ ] pull request trigger tests
- [ ] schedule trigger tests
- [ ] workflow errors/warnings reviewed and addressed

### Testing done 
(for each selected checkbox, the corresponding test results link should
be listed here)

Author: dkaras-splunk

.github/workflows/reusable-build-test-release.yml

@@ -45,7 +45,7 @@ on:
         description: "list of OS used for scripted input tests"
         type: string
         default: >-
-          ["ubuntu:16.04", "ubuntu:18.04", "ubuntu:20.04", "ubuntu:22.04", "ubuntu:24.04", "redhat:8.4", "redhat:8.5", "redhat:8.6", "redhat:8.8", "redhat:9.5"]
+          ["ubuntu:18.04", "ubuntu:20.04", "ubuntu:22.04", "ubuntu:24.04", "redhat:8.4", "redhat:8.5", "redhat:8.6", "redhat:8.8", "redhat:9.5"]
       upgrade-tests-ta-versions:
         required: false
         description: "List with TA versions (in 'X.X.X' format) that should be used as starting points for upgrade tests. Example: ['7.6.0', '7.7.0']"