Move CI to Xcode 26.4 (#1432)

Author: johnfairh

.github/workflows/Tests.yml

@@ -25,7 +25,7 @@ jobs:
           bundle exec danger --verbose
 
   spec:
-    runs-on: macos-15
+    runs-on: macos-26
     continue-on-error: true
     strategy:
       matrix:
@@ -37,7 +37,7 @@ jobs:
           persist-credentials: false
       - uses: maxim-lobanov/setup-xcode@v1
         with:
-          xcode-version: '26.2'
+          xcode-version: '26.4'
       - uses: ruby/setup-ruby@v1
         with:
           ruby-version: 3.3