small: eliminate unused variable warn on clang 15

Bump the small submodule with the following commit:

* https://github.com/tarantool/small/commit/02d3c23fd0d1e1743618850dc11378566b3804b1
  - It eliminates a CMake warning.
* https://github.com/tarantool/small/commit/c1ac3eef79a7394fb52442a77b958b66d82b8f0b
  - It adds on alloc/on truncate callbacks and poisoning of freed data.
    Tarantool 2.10 doesn't set the callbacks, so no behavior should
    change.
* https://github.com/tarantool/small/commit/5c3a0880ae4659cb662085563ff0b9eee40565fe
  - It eliminates the warning on clang 15.

See https://github.com/tarantool/small/issues/57
Part of #8110

It is a backport of PR #8142 for 2.10.

NO_DOC=build fix
NO_TEST=build fix
NO_CHANGELOG=to be added in a commit that fixes #8110