logback: remove static logger from Jooby class

jooby/src/main/java/io/jooby/Jooby.java

@@ -67,7 +67,7 @@ public class Jooby implements Router, Registry {
   static final String APP_NAME = "___app_name__";
 
   private static final String JOOBY_RUN_HOOK = "___jooby_run_hook__";
-  private static final Logger log = LoggerFactory.getLogger(Jooby.class);
+  private final Logger log = LoggerFactory.getLogger(Jooby.class);
 
   private final transient AtomicBoolean started = new AtomicBoolean(true);
 

jooby/src/test/java/io/jooby/Issue3963.java

@@ -0,0 +1,21 @@
+/*
+ * Jooby https://jooby.io
+ * Apache License Version 2.0 https://jooby.io/LICENSE.txt
+ * Copyright 2014 Edgar Espina
+ */
+package io.jooby;
+
+import static org.junit.jupiter.api.Assertions.assertFalse;
+
+import java.lang.reflect.Modifier;
+
+import org.junit.jupiter.api.Test;
+
+public class Issue3963 {
+
+  @Test
+  void logVariableCannotBeStatic() throws NoSuchFieldException {
+    var field = Jooby.class.getDeclaredField("log");
+    assertFalse(Modifier.isStatic(field.getModifiers()));
+  }
+}