add woodpecker build workflow

.woodpecker/build.yml

@@ -0,0 +1,8 @@
+when:
+  - event: "push"
+
+steps:
+  - name: "build"
+    image: "gradle:8.10.2-jdk21"
+    commands:
+      - "gradle build"

src/main/java/eu/e99/knockbat/KnockBat.java

@@ -56,4 +56,4 @@ public class KnockBat implements ModInitializer {
                 item
         );
     }
-}
+}