Unit test for appending to skipped rules

Unit test verifies fix for appending to skipped rules. One rules file
defines a rule with priority WARNING, a second rules file appends to
that rules file, and the configured priority is ERROR.

Ensures that falco rules without errors.

test/falco_tests.yaml

@@ -642,6 +642,14 @@ trace_files: !mux
       - rules/rule_append_failure.yaml
     trace_file: trace_files/cat_write.scap
 
+  rule_append_skipped:
+    detect: False
+    priority: ERROR
+    rules_file:
+      - rules/single_rule.yaml
+      - rules/append_single_rule.yaml
+    trace_file: trace_files/cat_write.scap
+
   rule_append:
     detect: True
     detect_level: WARNING
@@ -670,4 +678,4 @@ trace_files: !mux
     detect_level: INFO
     rules_file:
       - rules/detect_connect_using_in.yaml
-    trace_file: trace_files/connect_localhost.scap
+    trace_file: trace_files/connect_localhost.scap