build: add forgotten dependency to app-luatest

A full build compiles the dependency, but a `ctest` run after a partial
build may miss it. For example,

```sh
$ cmake . -DCMAKE_BUILD_TYPE=Debug
$ cmake --build . -j $(nproc) --target tarantool app-luatest-deps
$ ctest -j $(nproc) -L app-luatest -E http_client
```

And `test/app-luatest/tx_user_fiber_pool_test.lua` fails without
`test/app-luatest/lib/tx_user_fiber_pool.so`.

NO_DOC=fixes a specific way of testing harness run, not user-visible
NO_CHANGELOG=same

Author: Totktonada

test/app-luatest/CMakeLists.txt

@@ -13,7 +13,7 @@ message(STATUS "Add test suite ${TEST_SUITE_NAME}")
 # as a side effect.
 _add_test_suite_target(${TEST_SUITE_NAME}
   LABELS "${TEST_SUITE_NAME};regression;"
-  DEPENDS libyield
+  DEPENDS libyield tx_user_fiber_pool
 )
 
 list(APPEND TEST_ENV