video-transition: When using non crossfade effect use 'over' operations

For smptealph element to work as expected the following compositing
element should mix with the default "over" operator, as described
in its documentation.
13 jobs for transition_fixes in 41 minutes and 21 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Preparation
passed #317079
gst indent

00:00:19

passed #317078
manifest

00:00:38

 
  Build
passed #317080
build fedora x86_64

00:04:43

passed #317081
build nodebug fedora x86_64

00:04:57

 
  Test
passed #317082
check fedora

00:03:30

passed #317083
integration testsuites fedora

00:07:45

 
  Full Builds
passed #317085
build cerbero android universal

00:13:07

passed #317086
build cerbero cross win32

00:10:16

passed #317087
build cerbero cross win64

00:09:01

passed #317084
build cerbero fedora x86_64

00:09:33

 
  Full Tests
passed #317088
valgrind ges

00:04:15

 
  Apps
passed #317089
android universal examples

00:07:20

 
  Deploy
passed #317090
documentation

00:03:16