Add checkdepends to build xmlsec from source

xmlsec does not have a pypi prebuilt wheel on riscv64. Building from source requires these dependencies.

Fixes:

  creating '/tmp/pip-modern-metadata-s2wo_a6z/xmlsec-1.3.16.dist-info'
  Running command Preparing metadata (pyproject.toml)
  Building lxml version 6.0.0.
  Building without Cython.
  Error: Please make sure the libxml2 and libxslt development packages are installed.
  error: subprocess-exited-with-error
  
  × Preparing metadata (pyproject.toml) did not run successfully.
  │ exit code: 1
  ╰─> See above for output.

FAILED testing/test_integration.py::test_xmlsec_download_regression - Failed:...