fix macos image definitions and copying of the release assets

Author: hcannoodt

.github/workflows/prep_release.yml

@@ -16,7 +16,7 @@ jobs:
 
     steps:
     - name: Checkout code
-      uses: actions/checkout@v5
+      uses: actions/checkout@v6
 
     - name: Set up JDK 17
       uses: actions/setup-java@v5
@@ -82,9 +82,9 @@ jobs:
       fail-fast: false
       matrix:
         include:
-          - os: macos-13
+          - os: macos-15-intel
             label: macos-x86_64
-          - os: macos-14
+          - os: macos-15
             label: macos-aarch64
           - os: ubuntu-latest
             label: linux-x86_64
@@ -141,6 +141,7 @@ jobs:
       with:
         name: release-assets
         path: release-assets
+        merge-multiple: true
 
     - name: Download native binaries
       uses: actions/download-artifact@v4
@@ -154,9 +155,9 @@ jobs:
         mkdir -p release
 
         # JAR-based executable (backward compatible)
-        cp release-assets/bin/viash release/viash
-        cp release-assets/bin/schema.json release/schema.json
-        cp release-assets/bin/viash_install release/viash_install
+        cp release-assets/viash release/viash
+        cp release-assets/schema.json release/schema.json
+        cp release-assets/viash_install release/viash_install
 
         # Native binaries with platform suffixes
         cp native-binaries/viash-linux-x86_64/viash release/viash-linux-x86_64