bpo-34580: Update sqlite3 examples to call close() explicitly (GH-9079)

The sqlit3.Connection object doesn't call its close() method when it's used
as a context manager.
diff --git a/Doc/includes/sqlite3/md5func.py b/Doc/includes/sqlite3/md5func.py
index 0056b2d..16dc348 100644
--- a/Doc/includes/sqlite3/md5func.py
+++ b/Doc/includes/sqlite3/md5func.py
@@ -9,3 +9,5 @@
 cur = con.cursor()
 cur.execute("select md5(?)", (b"foo",))
 print(cur.fetchone()[0])
+
+con.close()