Final fix for windows (selfcheckouttest)

selfcheckout-example/src/main/resources/selfcheckout/receipts/testing/invalid_receipt.txt

-Egg, 6 stk;;breakfast
-;90.0;diary
-;90.0;
-;;
-Leverpostei;
\ No newline at end of file

selfcheckout-example/src/main/resources/selfcheckout/receipts/testing/test_receipt.txt

-null
-Egg, 6 stk;41.59;breakfast
-Hvitost, Synnøve;90.0;diary
-Leverpostei;29.99;breakfast
\ No newline at end of file

selfcheckout-example/src/test/java/selfcheckout/ReceiptHandlerTest.java

@@ -24,7 +24,7 @@ public abstract class ReceiptHandlerTest {
             Egg, 6 stk;41.59;breakfast
             Hvitost, Synnøve;90.0;diary
             Leverpostei;29.99;breakfast
-            """.replaceAll("\\R", "\n");
+            """.replaceAll("\\R", System.getProperty("line.separator"));
 
     private static final String invalid_receipt_file_content = """
             Egg, 6 stk;;breakfast
@@ -32,7 +32,7 @@ public abstract class ReceiptHandlerTest {
             ;90.0;
             ;;
             Leverpostei;
-            """.replaceAll("\\R", "\n");
+            """.replaceAll("\\R", System.getProperty("line.separator"));
 
     protected abstract IReceiptHandler getReceiptHandler();