testsuite: use sync_version if not none

Use sync_version from gst-validate-launcher
if it exists to use a custom version of the test suite

Part-of: <!92>
10 jobs for master in 2 minutes and 53 seconds (queued for 6 seconds)
Status Job ID Name Coverage
  Build Docker
passed #6044180
alpine amd64 manifest builder docker

00:00:17

passed #6044179
android docker

00:00:35

passed #6044178
cerbero fedora amd64 docker

00:00:52

passed #6044177
fedora amd64 docker

00:02:53

passed #6044181
gst-indent amd64 docker

00:01:22

 
  Preparation
manual #6044182
manual
manifest
 
  Test
created #6044183
gstreamer
integration testsuites fedora 1/4
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integration testsuites fedora 2/4
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integration testsuites fedora 3/4
created #6044186
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integration testsuites fedora 4/4