os: if dirFS.Open fails, undo use of backslashes in error message
This fixes a bug introduced by CL 426094 that caused the
golang.org/x/website/internal/web tests to fail.
Fixes #56034
Change-Id: Ic64967c6d440ad260b7283a18972b20023320ab6
Reviewed-on: https://go-review.googlesource.com/c/go/+/437976
Auto-Submit: Ian Lance Taylor <iant@google.com>
Run-TryBot: Ian Lance Taylor <iant@google.com>
Run-TryBot: Ian Lance Taylor <iant@golang.org> Reviewed-by: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org> Reviewed-by: Ian Lance Taylor <iant@google.com>