Clarify Governor events' lack of indexed parameters (#5175)

Co-authored-by: Hadrien Croubois <hadrien.croubois@gmail.com>

contracts/governance/IGovernor.sol

@@ -8,6 +8,9 @@ import {IERC6372} from "../interfaces/IERC6372.sol";
 
 /**
  * @dev Interface of the {Governor} core.
+ *
+ * NOTE: Event parameters lack the `indexed` keyword for compatibility with GovernorBravo events.
+ * Making event parameters `indexed` affects how events are decoded, potentially breaking existing indexers.
  */
 interface IGovernor is IERC165, IERC6372 {
     enum ProposalState {