SPI-2460: update xrootd

To run the testing, add a comment with:

Bot test PACKAGE[ PACKAGE2 ...]|all in TOOLCHAIN|all [(only|also) for LABEL-COMPILER-BUILDTYPE] please!

To ensure patches required for existing LCG branches are not lost, please add the respective labels: alsoTargeting:LCG_102-patches, alsoTargeting:master, etc.

cmake/toolchain/heptools-dev-base.cmake

@@ -826,7 +826,7 @@ LCG_external_package(XercesC           3.2.4        author=3.2.4
 LCG_external_package(xgboost           1.7.3                                    )
 LCG_external_package(xqilla            2.3.4                                    )
 LCG_external_package(xlrd              2.0.1                                    )
-LCG_external_package(xrootd            5.6.0                                    )
+LCG_external_package(xrootd            5.6.3                                    )
 LCG_external_package(xxHash            0.8.2                                    )
 LCG_external_package(xyzservices       2023.5.0                                 )
 LCG_external_package(xz                5.0.4                                    )