cerbero: Fix spawning of cerbero shell on Windows

This regressed in gstreamer/cerbero!154
10 jobs for fix-cerbero-shell in 111 minutes and 50 seconds (queued for 1 second)
Status Job ID Name Coverage
  Preparation
passed #243461
manifest

00:00:21

 
  Build
passed #243463
cerbero deps android universal

01:23:49

passed #243462
cerbero deps fedora x86_64

00:42:02

passed #243464
cerbero deps windows x86

00:36:36

passed #243465
cerbero deps windows x86_64

00:42:35

 
  Full Builds
passed #243467
cerbero android universal

00:19:45

passed #243468
cerbero cross win32

00:21:30

passed #243469
cerbero cross win64

00:08:44

passed #243466
cerbero fedora x86_64

00:05:51

 
  Apps
passed #243470
cerbero android universal examples

00:06:08