Fix: Use Xcode 26.3 (26.4 does not exist) and matching simulator OS

.github/workflows/build-debug.yml

@@ -76,7 +76,7 @@ jobs:
       - name: Setup Xcode
         uses: maxim-lobanov/setup-xcode@v1
         with:
-          xcode-version: '26.4'
+          xcode-version: '26.3'
 
       - name: Show Xcode version
         run: |
@@ -101,7 +101,7 @@ jobs:
             -project uuvpn.xcodeproj \
             -scheme SFI \
             -sdk iphonesimulator \
-            -destination 'platform=iOS Simulator,name=iPhone Air,OS=26.4' \
+            -destination 'platform=iOS Simulator,name=iPhone Air,OS=26.3' \
             -configuration Debug \
             CODE_SIGN_IDENTITY="" \
             CODE_SIGNING_REQUIRED=NO \