fix: Add missing robot:exit-on-failure tag to reserved tag list (#1712)

Author: bhirsz

src/robocop/linter/rules/tags.py

@@ -334,6 +334,7 @@ class TagNameChecker(VisitorChecker):
     is_keyword = False
     reserved_tags = {
         "robot:exit",
+        "robot:exit-on-failure",
         "robot:flatten",
         "robot:no-dry-run",
         "robot:continue-on-failure",