Fix remaining tag references in tests

- Update CacheRequest test to use version field
- Fix upload_test_file calls that still used tag parameter
- Update artifact history test to check versions instead of tags
- Update artifact stats tests to check versions instead of tags
- Fix garbage collection tests to delete versions instead of tags
- Remove TestGlobalTags class (endpoint removed)
- Update project/package stats tests to check version_count
- Fix upload_test_file fixture in test_download_verification

backend/tests/integration/test_projects_api.py

@@ -149,7 +149,7 @@ class TestProjectStats:
         assert "project_id" in data
         assert "project_name" in data
         assert "package_count" in data
-        assert "tag_count" in data
+        assert "version_count" in data
         assert "artifact_count" in data
         assert "total_size_bytes" in data
         assert "upload_count" in data