Update national reporting import spec to expose blank line bug

When a national reporting upload includes trailing blank lines
then these are being mistakenly counted in the "Out of <n> records"
summary.

Jira-Issue: MAV-3401

Author: mikejamesthompson

spec/fixtures/immunisation_import/national_reporting/valid_mixed_flu_hpv.csv

@@ -2,3 +2,4 @@
 RYG,100000,Hogwarts,9449308357,Harry,Potter,20010101,male,AA11 1AA,Y,20251109,AstraZeneca Fluenz LAIV,ABC123,20251030,Left Upper Arm,Albus,Dumbledore,,,Parental Consent,1234,ABCD,
 RYG,100000,,9999075320,Ron,Weasley,20010102,not knOWn,S1 1AA,,20251109,Gardasil,ABC123,20251030,nasal,,,,1,,1235,ABCE,community setting
 RYG,100000,,9990000018,Hermione,Granger,20010103,Female,S2 1AA,N,20251109,"","","","",,,,"",,1235,ABCE,""
+,,,,,,,,,,,,,,,,,,,,,,