test: Set PTS on proper variable

This would previously set the PTS on a random address causing various
memory corruption
8 jobs for memory-corruption in 17 minutes and 8 seconds (queued for 1 second)
Status Job ID Name Coverage
  Preparation
passed #92315
gst indent

00:00:39

passed #92314
manifest

00:00:43

 
  Build
passed #92316
build fedora x86_64

00:02:56

 
  Test
passed #92317
check fedora

00:03:24

 
  Full Builds
passed #92318
build android arm64 api28

00:04:43

passed #92320
build cerbero cross win32

00:10:03

passed #92321
build cerbero cross win64

00:08:20

passed #92319
build cerbero fedora x86_64

00:08:42