tests: lwm2m_registry: Add newlib filter to testcase.yaml

Not all toolchains support newlib so tests that require newlib need
to have a filter to we don't try and build those tests on those
testcases.  Add the following to testcase.yaml to handle the issue:

        filter: TOOLCHAIN_HAS_NEWLIB == 1

Fixes #54440

Signed-off-by: Kumar Gala <kumar.gala@intel.com>