Added swscale to FFMPEG build job

[ahmadsharif1]

Before this diff we were not building and creating swscale binaries to be uploaded to S3.

We will be explicitly depending on swscale after #205, so this diff is in preparation for that.

Note that swscale only depends on avutil so that's the only rpath we need to fix.

ldd /home/ahmads/.conda/envs/lerobot9/lib/libswscale.so | grep av
        libavutil.so.59 => /home/ahmads/.conda/envs/lerobot9/lib/./libavutil.so.59 (0x00007fef24000000)

tar xf ./2024-09-23/macos_arm64/7.0.1.tar.gz -C ffmpeg7                                                                                                                                                       

(base)
ahmads@ahmads-mbp ~/w/ffmpeg_build> ls                                                                                                                                                                                                            

(base)
2024-09-23/ ffmpeg7/

ahmads@ahmads-mbp ~/w/ffmpeg_build> find ffmpeg7/ | grep swscale                                                                                                                                                                                  (base)
ffmpeg7//ffmpeg/include/libswscale
ffmpeg7//ffmpeg/include/libswscale/version.h
ffmpeg7//ffmpeg/include/libswscale/swscale.h
ffmpeg7//ffmpeg/include/libswscale/version_major.h
ffmpeg7//ffmpeg/lib/libswscale.dylib
ffmpeg7//ffmpeg/lib/pkgconfig/libswscale.pc
ffmpeg7//ffmpeg/lib/libswscale.8.1.100.dylib
ffmpeg7//ffmpeg/lib/libswscale.8.dylib
ahmads@ahmads-mbp ~/w/ffmpeg_build> otool -L ffmpeg7//ffmpeg/lib/libswscale.8.dylib                                                                                                                                                               

(base)
ffmpeg7//ffmpeg/lib/libswscale.8.dylib:
	@rpath/libswscale.8.dylib (compatibility version 8.0.0, current version 8.1.100)
	@rpath/libavutil.59.dylib (compatibility version 59.0.0, current version 59.8.100)
	/usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1345.100.2)
	/System/Library/Frameworks/CoreFoundation.framework/Versions/A/CoreFoundation (compatibility version 150.0.0, current version 2419.0.0)
	/System/Library/Frameworks/CoreVideo.framework/Versions/A/CoreVideo (compatibility version 1.2.0, current version 1.5.0)
	/System/Library/Frameworks/CoreMedia.framework/Versions/A/CoreMedia (compatibility version 1.0.0, current version 1.0.0)

[scotts]

Looks good to me. @ahmadsharif1, before merging, can you do the kind of check I did in #211? That is, your command is doing ldd on a .so is for Linux. The commands from my PR show how to do it on Mac for a .dylib from artifact generated by the GitHub Action.

[ahmadsharif1]

@scotts I updated the top comment. PTAL.