ADDON-89264: fix: generate Swagger artifacts independently of UCC test selection

[rasteja]

Summary

Generate and publish Swagger artifacts for add-ons with UCC modinput tests even when the UCC test job is not selected.

Root cause

Swagger artifact upload was tied to execute-ucc_modinput. When that test job was skipped, TACO later failed because the build-specific S3 prefix did not contain swagger_client.

Changes

• Detect whether tests/ucc_modinput_functional exists.
• Use that capability, rather than test selection, when uploading and downloading the OpenAPI artifact.
• Preserve existing UCC test-selection behavior.

Validation

• Parsed workflow YAML.
• Ran diff whitespace checks.

Related

• ADDON-89264