Try basing the GH release on github.ref_name instead of github.ref.

Using github.ref as action-gh-release's target_commitish produces:

 GitHub release failed with status: 422
[{"resource":"Release","code":"invalid","field":"target_commitish"}]

.github/workflows/build.yaml

@@ -382,7 +382,7 @@ jobs:
             ${{ needs.build.outputs.relnotes }}
           prerelease: true
           generate_release_notes: true
-          target_commitish: ${{ github.ref }}
+          target_commitish: ${{ github.ref_name }}
           append_body: true
           fail_on_unmatched_files: true
           files: |