Use Xcode version 15.4.0

Author: arik-so

.github/workflows/build-xcframework-sequential.yml

@@ -22,13 +22,13 @@ jobs:
         name: Build libldks, build xcarchives, and combine into xcframework
         runs-on: macos-latest
         env:
-            DEVELOPER_DIR: /Applications/Xcode_16.2.0.app/Contents/Developer
+            DEVELOPER_DIR: /Applications/Xcode_15.4.0.app/Contents/Developer
             LDK_C_BINDINGS_BASE: ${{ github.workspace }}/bindings/artifacts/ldk-c-bindings
         steps:
             -   name: Configure Xcode
                 uses: maxim-lobanov/setup-xcode@v1
                 with:
-                    xcode-version: latest
+                    xcode-version: 15.4.0
             -   name: Print Xcode SDK availability
                 shell: bash
                 run: |