fix: Added missing getter and setter for the problemFile in the FileProblemProvider

Author: Magnus Raagaard Kjeldsen

benchmark/src/main/java/ai/timefold/solver/benchmark/impl/loader/FileProblemProvider.java

@@ -74,4 +74,11 @@ public String toString() {
         return problemFile.toString();
     }
 
+    public File getProblemFile() {
+        return problemFile;
+    }
+
+    public void setProblemFile(File problemFile) {
+        this.problemFile = problemFile;
+    }
 }