fix: formatting of plot-title in placeholder (#4702)

Author: PierreSchwang

Core/src/main/java/com/plotsquared/core/plot/PlotTitle.java

@@ -63,4 +63,18 @@ public String subtitle() {
         return subtitle;
     }
 
+    /**
+     * Provides a string representation of this plot title value (used in placeholders).
+     *
+     * @return the plot title representation in the format {@code "<title>" "<subtitle>"}
+     * @since TODO
+     */
+    @Override
+    public String toString() {
+        return "\"%s\" \"%s\"".formatted(
+                this.title != null ? this.title : "",
+                this.subtitle != null ? this.subtitle : ""
+        );
+    }
+
 }