Regex: add unit test for #1693

src/regex_impl.cc

@@ -1388,6 +1388,11 @@ auto test_regex = UnitTest{[]{
         kak_assert(vm.exec("abcde"));
     }
 
+    {
+        TestVM<> vm{R"((?i)[a-c]+)"};
+        kak_assert(vm.exec("bCa"));
+    }
+
     {
         TestVM<> vm{R"(д)"};
         kak_assert(vm.exec("д", RegexExecFlags::Search));