Override github.com/xi2/xz license (#2711)

* Override github.com/xi2/xz license

* Set the license to Unlicense

Author: romulets

.buildkite/scripts/generate_notice.py

@@ -31,6 +31,7 @@
     {"name": "github.com/spdx/tools-golang", "licenceFile": "LICENSE.code", "licenceType": "Apache-2.0"},
     {"name": "github.com/aquasecurity/trivy-policies", "licenceType": "MIT"},
     {"name": "github.com/csaf-poc/csaf_distribution/v3", "licenceType": "Apache-2.0"},
+    {"name": "github.com/xi2/xz", "licenceType": "Unlicense"},
 ]
 
 # Additional third-party, non-source code dependencies, to add to the CSV output.