Take the bigger amount of rebuilds from supported linux arches

[samueldr]

nixpkgs#63147 is marked as having 0 Linux rebuilds, but has 587 changed paths, all aarch64-only.

The way the labels are currently reporting the stats makes it seem like this is a complete no-op. This instance is small, but a large aarch64 only rebuild might be easily missed.

I'm thinking that the amount for the label might be better represented as max(x86_64-linuxRebuilds, aarch64-linuxRebuilds) for Linux.

[sternenseemann]

Also stuff like https://github.com/NixOS/nixpkgs/pull/348568 is misrepresented where there a few x86_64, but a lot of aarch64 rebuilds.

[lilyinstarlight]

There was #684 which was tested and would solve this, but no one seemed interested

[wolfgangwalther]

This has been solved properly in nixpkgs' GHC workflows.