use macos-26 runner (has Xcode 26 with Swift 6.2)

Author: lucasfischer

.github/workflows/test-release.yml

@@ -25,7 +25,7 @@ concurrency:
 
 jobs:
   release:
-    runs-on: macos-15
+    runs-on: macos-26
     steps:
       - uses: actions/checkout@v4