Update macOS runners to macos-latest in release workflow

### Fixes
- Replace deprecated macos-13 and macos-14 runners with macos-latest
- macOS-13 runner has been retired by GitHub
- Bun supports cross-compilation, allowing darwin-x64 builds from ARM64 runners

Author: llbbl

.github/workflows/release.yml

@@ -20,10 +20,10 @@ jobs:
             os: ubuntu-latest
             artifact: upkeep-linux-x64
           - target: darwin-arm64
-            os: macos-14
+            os: macos-latest
             artifact: upkeep-darwin-arm64
           - target: darwin-x64
-            os: macos-13
+            os: macos-latest
             artifact: upkeep-darwin-x64
           - target: windows-x64
             os: windows-latest