Normally you run lit tests against a ninja build. So you build Xcode to work on a nice IDE, and for running lit tests you use a ninja build that I normally use:
// Ninja Build command
./swift/utils/build-script --release --skip-build-benchmarks --swift-darwin-supported-archs 'x86_64' --sccache --skip-ios --skip-tvos --skip-watchos
// And then for Testing
llvm-project/llvm/utils/lit/lit.py -sv --param swift_site_config=build/Ninja-ReleaseAssert/swift-macosx-x86_64/test-macosx-x86_64/lit.site.cfg swift/test/
Note that the folder x86_64 may be different if you are building on a M1 Mac ...
But for lit tests I always used the ninja build, because as far as I know it will not work on Xcode one ... so in short you have to build both ninja and Xcode, and run lit against the ninja one =]
This target I think will run the UnitTests(cpp unit tests under unittests folder) not the test/** that we run using lit. But this error is already tracked on an issue [SR-14352] Xcode fails to run Swift unittests · Issue #56711 · apple/swift · GitHub and I'm not sure, but maybe https://github.com/apple/swift/pull/36971 will fix it ...