buffer: add test for gst_buffer_foreach_meta

Existing tests for iterating/removing buffer meta data were insufficient
to detect linked list corruption when removing multiple metas.  Added a
test to validate fix from 54150f5d for issue #332.
3 jobs for gstbuffer-foreach-tests in 4 minutes and 5 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Preparation
passed #54684
manifest

00:00:19

 
  Build
passed #54685
build fedora x86_64

00:01:22

 
  Full Builds
passed #54686
build android arm64 api28

00:02:23