fix(sqitch-ci): uniq should be applied on sorted text

.bin/sqitch-check-immutable-files.sh

@@ -11,7 +11,7 @@ changes_after_last_tag=$(tac "${1}"/sqitch.plan | sed '/^@/Q' | cut -d' ' -f1)
 
 # comm compares two ordered files and returns three columns "-23" suppresses colums 2 and 3,
 # so it only returns the first column (the lines unique to file 1)
-immutable_modified_files=$(comm -23 <(echo "$modified_changes" | uniq | sort) <(echo "$changes_after_last_tag" | sort))
+immutable_modified_files=$(comm -23 <(echo "$modified_changes" | sort | uniq) <(echo "$changes_after_last_tag" | sort | uniq))
 if [ -n "$immutable_modified_files" ]; then
   echo "The following sqitch changes are immutable as they are part of a tagged release. Please add incremental changes instead."
   echo "$immutable_modified_files"