Fix CI: restore memoryinterface doc anchor (gh-105766)

The PR renamed the Memory Interface section label to mem-interface,
breaking external links to c-api/memory.html#memoryinterface. Keep
both labels on the section.

Co-authored-by: Muse Code (Meta Muse Spark)

Author: Muse Code

Doc/c-api/memory.rst

@@ -224,6 +224,7 @@ zero bytes.
 
 
 .. _mem-interface:
+.. _memoryinterface:
 
 Memory Interface
 ================