ci(release): add registry credentials from secret

Signed-off-by: Vojtěch Mareš <vojtech@mares.cz>

.woodpecker/release.yaml

@@ -18,6 +18,12 @@ steps:
             repo: *repo
             platforms: *platforms
             tag: next
+            logins:
+                - registry: https://registry.mareshq.com
+                  username:
+                      from_secret: docker_username
+                  password:
+                      from_secret: docker_password
         when:
             branch: main
             event: push