glcolorbalance: Copy caps in transform_internal_caps()

We don't get ownership of the caps that are passed in, and doing so
causes crashes at a later time.

Fixes gstreamer/gst-plugins-base#546
8 jobs for <span class="ref-name">glcolorbalance-caps-crash</span> in 17 minutes and 49 seconds (queued for 1 second)
Status Job ID Name Coverage
  Preparation
passed #88579
gst indent

00:00:39

passed #88578
manifest

00:00:39

 
  Build
passed #88580
build fedora x86_64

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  Test
passed #88581
check fedora

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  Full Builds
passed #88582
build android arm64 api28

00:05:20

passed #88584
build cerbero cross win32

00:09:54

passed #88585
build cerbero cross win64

00:08:58

passed #88583
build cerbero fedora x86_64

00:09:06