catch_discover_tests causes XCode build to fail spuriously

**Describe the bug**
When building with XCode on MacOS, the build will occasionally fail spuriously when running the script added by `catch_discover_tests` (the error in XCode is "PhaseScriptExecution failed"), but will then succeed when re-running the build.

**Expected behavior**
The build should succeed without needing to be re-run.

**Reproduction steps**
This issue is present in my [Limes library](https://github.com/benthevining/Limes), which can be built with:
```sh
cmake --preset xcode
cmake --build --preset xcode
```
I can try to create a minimal repro if needed.

**Platform information:**
- OS: MacOS
- Compiler+version: AppleClang
- Catch version: Latest (tip of devel)
- CMake generator: Xcode