Update ERC-7786: Add background to diagram

Merged by EIP-Bot.

Author: ernestognw

ERCS/erc-7786.md

@@ -140,7 +140,7 @@ MUST return `IERC7786Receiver.executeMessage.selector` (`0x675b049b`).
 
 #### Interaction Diagram
 
-![](../assets/eip-7786/send-execute.svg)
+![](../assets/eip-7786/send-execute.png)
 
 ### Properties