Updating the xrootd client to 5.6.9 to mitigate https://github.com/xrootd/xrootd/issues/2082. Uses https://github.com/spack/spack/commit/62132919e1465a40e3522e40278e4bbc8ec32978.
https://github.com/spack/spack/commit/27c8135207d27015181c3b093e5bd37146e801b1 https://github.com/spack/spack/commit/082afe04b84c201f84b4d9cf9bdc8e3e8dbdeb8f
