rules_swift 3.4.1 fails on rules_xcodeproj generated projects

When using the latest rules_swift (3.4.1), generating an xcode project using rules_xcodeproj results in a project that can't build. That seems to happen because of [this line](https://github.com/bazelbuild/rules_swift/blob/main/tools/worker/swift_runner.cc#L330), and only if using sandboxing. Setting ENABLE_CODE_COVERAGE to NO in the Xcode project fixes it. Here is the error: `libc++abi: terminating due to uncaught exception of type std::__1::__fs::filesystem::filesystem_error: filesystem error: in canonical: No such file or directory [".../rules_xcodeproj.noindex/build_output_base/sandbox/darwin-sandbox/817/execroot/_main/BUILD.bazel"] [""]`