mdbx-test: add registry for test cases.

Change-Id: Ie9f069dbe6846af170628945db9897ec690fc3da

test/try.cc

@@ -1,5 +1,13 @@
 #include "test.h"
 
+class testcase_try : public testcase {
+public:
+  testcase_try(const actor_config &config, const mdbx_pid_t pid)
+      : testcase(config, pid) {}
+  bool run() override;
+};
+REGISTER_TESTCASE(try);
+
 bool testcase_try::run() {
   db_open();
   assert(!txn_guard);