Please make builds reproducible

[jlaine]

Looking at the output of successive builds for the same build scripts I noticed that the output artifacts do not match, for example the two latest runs:

• https://github.com/PyAV-Org/pyav-ffmpeg/actions/runs/13406535926
• https://github.com/PyAV-Org/pyav-ffmpeg/actions/runs/13405555722

The "7a-community" release binary seems to be the one from the "patch" build, not the "main" build.

=> why are the outputs not the same?

[WyattBlue]

I see the file sizes changing.

for "Disable experimental codecs" MacOS arm64 artifact size:
27461719 - on patch
27467618 - on main

I'm not sure why this is happening (maybe it's race conditions in make for parallel builds), but I'm not surprised by this. I'm also not sure if there's anything we can do besides, uggh, NixOS, or disable all parallel builds.