Update vendored dependency to fix build error
The vendored version of `jansson` no longer builds with latest
`cmake.4.2.3`:
```
File "ocaml-jansson/src/c/dune", lines 79-119, characters 0-1253:
79 | (rule
80 | (deps
81 | (source_tree %{project_root}/vendor/jansson))
.....
117 | (copy
118 | %{project_root}/vendor/jansson/build/lib/libjansson%{ext_lib}
119 | %{project_root}/src/c/libjansson.a)))))))))
-- Configuring incomplete, errors occurred!
CMake Error at CMakeLists.txt:49 (cmake_minimum_required):
Compatibility with CMake < 3.5 has been removed from CMake.
Update the VERSION argument <min> value. Or, use the <min>...<max> syntax
to tell CMake that the project requires at least <min> but has been updated
to work with policies introduced by <max> or earlier.
Or, add -DCMAKE_POLICY_VERSION_MINIMUM=3.5 to try configuring anyway.
```
Bump the vendored code to its latest version, which fixes this build
error.
Signed-off-by: Edwin Török <edwin@tarides.com>