Windows: Fix symlink privilege error detection

The message is in e.args[1] and not e.args[0] at least with python 3.8.
Should be more future proof like this in case it change again.
11 jobs for win-symlink in 7 minutes and 36 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Build
passed #7316574
meson android arm64 fedora

00:01:20

passed #7316572
gst-macos-10.15
meson macos

00:03:03

passed #7316569
meson-mingw-w64-build

00:05:32

manual #7316573
docker windows 1809 allowed to fail manual
meson msys2
passed #7316567
meson-shared-build

00:04:43

passed #7316568
meson-static-build

00:05:37

passed #7316570
docker windows 1809
meson vs2017 amd64

00:01:27

passed #7316571
docker windows 1809
meson vs2017 x86

00:01:27

passed #7316566
mingw-build

00:06:55

passed #7316564
shared-build

00:07:36

passed #7316565
static-build

00:04:27