os: check for valid Windows path when creating files

os: check for valid Windows path when creating files

Checks for a valid Windows path by ensuring the path doesn't end with trailing spaces or periods.

Fixes #54040.

Cq-Include-Trybots: luci.golang.try:gotip-windows-arm64
Change-Id: I266f79963c821f8cc474097d3e57c5645ad996fc
Reviewed-on: https://go-review.googlesource.com/c/go/+/618496
Reviewed-by: Quim Muntal <quimmuntal@gmail.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Damien Neil <dneil@google.com>
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>
Reviewed-by: Carlos Amedee <carlos@golang.org>