ci(docker): Fix caching (#2391)

Because we are building two different Docker containers (one for each
platform), we need separate caches for each one, otherwise both builds
use the same cache, resulting in them overwriting each other. By setting
a [separate scope for
each,](https://docs.docker.com/build/cache/backends/gha/#scope)
 the caches will be separate and not overwrite each other.

.github/workflows/build.yml

@@ -296,8 +296,8 @@ jobs:
           push: true
           platforms: linux/${{ matrix.platform }}
           tags: ghcr.io/${{ github.repository }}:${{ github.sha }}-${{ matrix.platform }}
-          cache-from: type=gha
-          cache-to: type=gha,mode=max
+          cache-from: type=gha,scope=${{ matrix.platform }}
+          cache-to: type=gha,mode=max,scope=${{ matrix.platform }}
 
   multiarch-docker:
     name: Create Multi-Architecture Docker Image