Rename job to "xcodebuild" and add new job "ios"

- The commit renames the job "build" to "xcodebuild" in the build.yml file.
- It also adds a new job "ios" to the build.yml file.
- Both jobs run on "macos-13" and include steps for code checkout and Xcode build.
- The "xcodebuild" job tests the "katago" scheme in the cpp/xcode directory.
- The "ios" job builds the "KataGo iOS" scheme in the ios/KataGo iOS directory.

.github/workflows/build.yml

@@ -6,7 +6,7 @@ on:
       - '.github/workflows/build.yml'
 
 jobs:
-  build:
+  xcodebuild:
     runs-on: macos-13
     steps:
     - name: Checkout code
@@ -44,3 +44,15 @@ jobs:
       run: |
         cd cpp/xcode
         /Applications/Xcode_15.0.1.app/Contents/Developer/usr/bin/xcodebuild -derivedDataPath DerivedData -scheme katago -configuration Release test
+
+  ios:
+    runs-on: macos-13
+    steps:
+    - name: Checkout code
+      uses: actions/checkout@v3
+
+    - name: Run Xcode build
+      run: |
+        cd "ios/KataGo iOS"
+        /Applications/Xcode_15.0.1.app/Contents/Developer/usr/bin/xcodebuild -derivedDataPath DerivedData -scheme "KataGo iOS" -configuration Release build
+