Fix release workflow: clear SPM cache before build

.github/workflows/release.yml

@@ -50,6 +50,11 @@ jobs:
           rm -rf GhosttyKit.xcframework
           cp -R ghostty/macos/GhosttyKit.xcframework GhosttyKit.xcframework
 
+      - name: Clear SPM cache
+        run: |
+          rm -rf ~/Library/Caches/org.swift.swiftpm
+          rm -rf ~/Library/Developer/Xcode/DerivedData
+
       - name: Build app (Release)
         env:
           SPARKLE_PUBLIC_KEY: ${{ secrets.SPARKLE_PUBLIC_KEY }}