Assert that we don't get the value we don't want instead of attemptin…

…g to check for a specific error code. Fixes dotnet#39955 (dotnet#40019)

src/libraries/System.IO.FileSystem/tests/Enumeration/ErrorHandlingTests.cs

@@ -73,8 +73,11 @@ public void NotFoundErrorIsExpected()
  // Make sure we're returning the native error as expected (and not the PAL error on Unix)
  using (LastError le = new LastError(Path.GetRandomFileName()))
  {
- // Conveniently ERROR_FILE_NOT_FOUND and ENOENT are both 0x2
- Assert.Equal(2, le.Error);
+ // while ERROR_FILE_NOT_FOUND/ENOENT have predictable values on Windows, Linux and Mac,
+ // we can't rely on ENOENT having the same value on other platforms. Instead, assert
+ // that we didn't get the PAL error because we know its value.
+ const int PAL_Error_ENOENT = 0x1002D;
+ Assert.NotEqual(PAL_Error_ENOENT, le.Error);
  }
  }