Fix Sparkle tools version to 2.8.1

2.7.5 doesn't exist, causing tar extraction to fail.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: jsflax

.github/workflows/release.yml

@@ -180,7 +180,7 @@ jobs:
           DMG="MemoryVisualizer-${VERSION}.dmg"
 
           # Download Sparkle tools
-          SPARKLE_VERSION="2.7.5"
+          SPARKLE_VERSION="2.8.1"
           curl -sL "https://github.com/sparkle-project/Sparkle/releases/download/${SPARKLE_VERSION}/Sparkle-${SPARKLE_VERSION}.tar.xz" | tar xJ -C /tmp/sparkle-tools bin/
 
           # Move DMG to a staging dir for generate_appcast