add: xcode version handling on ci

Author: mflknr

.github/workflows/builds.yml

@@ -18,6 +18,9 @@ jobs:
     runs-on: ${{ matrix.os }}
     steps:
       - uses: actions/checkout@v4
+      - uses: maxim-lobanov/setup-xcode@v1
+        with:
+          xcode-version: '15.2.0'
       - uses: fwal/setup-swift@v2
         with:
           swift-version: ${{ matrix.swift }}