drone: use official drone-scp image again

Our PR got accepted and the flag we needed is available now:
https://github.com/appleboy/drone-scp/pull/102

.drone.yml

@@ -111,9 +111,8 @@ steps:
       - nix run nixpkgs#gnused -- --in-place "s/$ISO_NAME/PubSolarOS-latest.iso/" PubSolarOS-latest.iso.sha256
 
   - name: "Publish ISO"
-    # custom drone-scp image, source: https://git.b12f.io/pub-solar/drone-scp/
-    # docker build --tag registry.greenbaum.cloud/library/drone-scp:v1.6.5 --file ./docker/Dockerfile.linux.amd64 .
-    image: registry.greenbaum.cloud/library/drone-scp:v1.6.5
+    # https://github.com/appleboy/drone-scp/pull/141 got merged, yay
+    image: appleboy/drone-scp:1.6.5-linux-amd64
     volumes:
       - name: file-exchange
         path: /var/nix/iso-cache
@@ -148,6 +147,6 @@ volumes:
 
 ---
 kind: signature
-hmac: 0c0994f0878cdb49172772f78c9a772f5c75830b49c1c22bd15db385fe857e17
+hmac: d6187b243c1939eaf2803830e784aa89dd20edda9ba205940cf6caa2c615b6c6
 
 ...