Fix compatibility with Boost 1.81

This fixes occurrences in LHCb of he same problem reported in gaudi/Gaudi#255 (closed)

Hlt/HltServices/src/ConfigFileAccessSvc.cpp

@@ -113,7 +113,7 @@ PropertyConfig::digest_type ConfigFileAccessSvc::writePropertyConfig( const Prop
   PropertyConfig::digest_type digest = config.digest();
 
   fs::path fnam = propertyConfigPath( digest );
-  fs::path fdir = fnam.branch_path();
+  fs::path fdir = fnam.parent_path();
   if ( !fs::exists( fdir ) && !create_directories( fdir ) ) {
     error() << " directory " << fdir.string() << " does not exist, and could not create... " << endmsg;
     return PropertyConfig::digest_type::createInvalid();
@@ -138,7 +138,7 @@ ConfigTreeNode::digest_type ConfigFileAccessSvc::writeConfigTreeNode( const Conf
   ConfigTreeNode::digest_type digest = config.digest();
 
   fs::path fnam = configTreeNodePath( digest );
-  fs::path fdir = fnam.branch_path();
+  fs::path fdir = fnam.parent_path();
   if ( !fs::exists( fdir ) && !create_directories( fdir ) ) {
     error() << " directory " << fdir.string() << " does not exist, and could not create... " << endmsg;
     return ConfigTreeNode::digest_type::createInvalid();
@@ -174,7 +174,7 @@ ConfigTreeNodeAlias::alias_type ConfigFileAccessSvc::writeConfigTreeNodeAlias( c
   }
   // now write alias...
   fs::path fnam = configTreeNodeAliasPath( alias.alias() );
-  fs::path fdir = fnam.branch_path();
+  fs::path fdir = fnam.parent_path();
   if ( fs::exists( fdir ) ) {
     if ( !isCompatible( alias, fdir ) ) {
       error() << " current TOPLEVEL is not compatible with other config in " << fdir.string()