Fix code-start headers in documentation

Author: Marenz

docs/contracts/events.rst

@@ -73,7 +73,7 @@ four indexed arguments rather than three.
     In particular, it is possible to "fake" the signature of another event
     using an anonymous event.
 
-::
+.. code-block:: solidity
 
     // SPDX-License-Identifier: GPL-3.0
     pragma solidity >=0.4.21 <0.9.0;

docs/natspec-format.rst

@@ -58,7 +58,7 @@ The following example shows a contract and a function using all available tags.
 
   This may change in the future.
 
-.. code:: Solidity
+.. code-block:: Solidity
 
     // SPDX-License-Identifier: GPL-3.0
     pragma solidity >=0.8.2 < 0.9.0;