test-execute: add a test for systemcall filter (#10273)

This adds a test for issue #9939 which is fixed by
a5404992cc (#9942).

src/test/test-execute.c

@@ -359,6 +359,7 @@ static void test_exec_systemcallfilter(Manager *m) {
 
         test(m, "exec-systemcallfilter-with-errno-name.service", errno_from_name("EILSEQ"), CLD_EXITED);
         test(m, "exec-systemcallfilter-with-errno-number.service", 255, CLD_EXITED);
+        test(m, "exec-systemcallfilter-with-errno-multi.service", errno_from_name("EILSEQ"), CLD_EXITED);
 #endif
 }