docs: Force highlighter to work despite errors on snippets that it cannot parse

docs/contracts/libraries.rst

@@ -130,6 +130,7 @@ internal functions in libraries in order to implement
 custom types without the overhead of external function calls:
 
 .. code-block:: solidity
+    :force:
 
     // SPDX-License-Identifier: GPL-3.0
     pragma solidity >=0.6.8 <0.9.0;