upgrade FFmpeg to v7 in build-melt.sh

Author: ddennedy

build/build-melt.sh

@@ -44,7 +44,7 @@ LIBVPX_REVISION=
 ENABLE_LAME=1
 FFMPEG_PROJECT="FFmpeg"
 FFMPEG_HEAD=0
-FFMPEG_REVISION="origin/release/6.1"
+FFMPEG_REVISION="origin/release/7.0"
 FFMPEG_SUPPORT_H264=1
 FFMPEG_SUPPORT_H265=1
 FFMPEG_SUPPORT_LIBVPX=1