ci/clang: Enable bundled FFmpeg

Explicitly use the bundled FFmpeg version, since we were auto-choosing
it before.

.ci/scripts/clang/docker.sh

@@ -19,6 +19,7 @@ cmake .. \
       -DENABLE_QT_TRANSLATION=ON \
       -DUSE_DISCORD_PRESENCE=ON \
       -DYUZU_ENABLE_COMPATIBILITY_REPORTING=${ENABLE_COMPATIBILITY_REPORTING:-"OFF"} \
+      -DYUZU_USE_BUNDLED_FFMPEG=ON \
       -GNinja
 
 ninja