Disable GLib deprecation warnings on stable cycles

Development cycles are the point in time when deprecations ought to be
addresses; stable cycles don't really need these warnings.
8 jobs for deprecation-error in 44 minutes and 27 seconds (queued for 1 minute and 53 seconds)
latest
Status Job ID Name Coverage
  Preparation
passed #186775
gst indent

00:00:40

passed #186774
manifest

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  Build
passed #186776
build fedora x86_64

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  Test
passed #186777
check fedora

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  Full Builds
passed #186779
build cerbero android universal

00:21:11

passed #186780
build cerbero cross win32

00:11:40

passed #186781
build cerbero cross win64

00:09:11

passed #186778
build cerbero fedora x86_64

00:09:52