Updated libsql_extensions.md fix broken link (#1044)

Fixed broken link to `wal.h`

Author: a2xchip

libsql-sqlite3/doc/libsql_extensions.md

@@ -291,7 +291,7 @@ Write-ahead log is a journaling mode which enables nice write concurrency charac
 ### API
 
 In order to register a new set of virtual WAL methods, these methods need to be implemented. This is the current API:
-https://github.com/libsql/libsql/blob/main/src/wal.h
+https://github.com/tursodatabase/libsql/blob/main/libsql-sqlite3/src/wal.h
 
 ### Registering WAL methods