Update submodule version to 2e89e24

This change is intended to resolve the issue when cmake 3.20+ is
installed in your system and in this case it's impossible to build
the mysql module because the following error occurs:

    CMake Error at mariadb-connector-c/cmake/ConnectorName.cmake:30 (ENDMACRO):
      Flow control statements are not properly nested.
    Call Stack (most recent call first):
      mariadb-connector-c/CMakeLists.txt:391 (INCLUDE)

So this patch updates the mariadb-connector-c submodule to the version
where the fix to resolve the mentioned error is applied.

Fixes #59

Author: ylobankov