Some syntax tree tests fail in Debug

https://github.com/dotnet/fsharp/pull/15343 introduced test failures when using Debug solution configuration:

```
System.AggregateException : One or more errors occurred. (One or more errors occurred. (Unknown exception seen in compiler: JetBrains.ReSharper.TestRunner.Logging.TraceListener+AssertionException: Unknown exception seen in compiler: JetBrains.ReSharper.TestRunner.Logging.TraceListener+AssertionException: Unexpected exception raised in compiler: value does not have a valid member type
FSharp.Compiler.DiagnosticsLogger+InternalError: value does not have a valid member type(5,8--5,9)

at FSharp.Compiler.ParseAndCheckInputs.CheckOneInput@1276-2.Invoke(CancellationToken ct) in C:\Developer\fsharp-main-5\src\Compiler\Driver\ParseAndCheckInputs.fs:line 1346
at FSharp.Compiler.ParseAndCheckInputs.CheckOneInput@1275-17.Invoke(CancellationToken ct)

at FSharp.Compiler.CodeAnalysis.ParseAndCheckFile.CheckOneFile@2690-6.Invoke(CancellationToken ct) in C:\Developer\fsharp-main-5\src\Compiler\Service\FSharpCheckerResults.fs:line 2693
at FSharp.Compiler.CodeAnalysis.ParseAndCheckFile.CheckOneFile@2680-8.Invoke(CancellationToken ct)
))
```

cc @T-Gro Could you please take a look?

I really wonder, why doesn't it fail in Release? Why doesn't it fail on CI?