Apply antora customization in more cases: when build_antora.sh is present.

Author: sdarwin

ci_boost_release.py

@@ -500,9 +500,10 @@ def command_build(self):
 
         os.chdir(self.root_dir)
         for directoryname in glob.iglob("libs/*", recursive=False):
-            if os.path.isdir(directoryname) and os.path.isfile(
-                os.path.join(directoryname, "doc", "antora_docs.sh")
-            ):  # filter dirs
+            if os.path.isdir(directoryname) and (
+                os.path.isfile(os.path.join(directoryname, "doc", "antora_docs.sh"))
+                or os.path.isfile(os.path.join(directoryname, "doc", "build_antora.sh"))
+            ):
                 antora_libraries.append(directoryname)
 
         utils.check_call(