fix(ci): add woodpecker 3 syntax

.woodpecker.yml

@@ -3,7 +3,7 @@ steps:
     image: gitnet.fr/deblan/mkdocs
     pull: true
     environment:
-      - SITE_URL=https://doc.murph-project.org/
+      SITE_URL: https://doc.murph-project.org/
     commands: |
       if [ -n "$SITE_URL" ]; then
         sed -i "s,# site_url: \"{site_url}\",site_url: \"$SITE_URL\"," mkdocs.yml
@@ -12,7 +12,9 @@ steps:
 
   commit:
     image: alpine/git
-    secrets: [ssh_private_key]
+    environment:
+      SSH_PRIVATE_KEY:
+        from_secret: ssh_private_key
     commands:
       - eval $(ssh-agent -s)
       - echo "$SSH_PRIVATE_KEY" | tr -d '\r' | ssh-add -