ci: bake cached toolchain into Podman agent and fix nested Buildah [CI]

.woodpecker/linux-release.yml

@@ -31,7 +31,7 @@ steps:
   - name: linux-amd64-backend
     image: bash
     environment:
-      NUGET_PACKAGES: /home/justme/.nuget/packages
+      NUGET_PACKAGES: /home/justme/woodpecker/cache/nuget/packages
       ZOT_REGISTRY: registry.oeo.one
       ZOT_USERNAME: justme
       ZOT_SECRET:
@@ -44,7 +44,7 @@ steps:
   - name: linux-arm64-backend
     image: bash
     environment:
-      NUGET_PACKAGES: /home/justme/.nuget/packages
+      NUGET_PACKAGES: /home/justme/woodpecker/cache/nuget/packages
       ZOT_REGISTRY: registry.oeo.one
       ZOT_USERNAME: justme
       ZOT_SECRET: