docs: Updated ISC Summit CfP Date

Based on announcement:
https://www.linkedin.com/feed/update/urn:li:activity:7346915290934374400

Author: Guilherme Dellagustin

content/en/events/isc-2025.md

@@ -40,7 +40,7 @@ This special 24-hour global event celebrates our 10th anniversary with sessions
 
 Each presentation will be delivered live, lasting approximately 20 minutes, followed by a brief discussion. Speakers should plan to present live and, if possible, in person at one of our event locations.
 
-Proposal submissions are due by **5PM GMT on Monday, July 15th**.
+Proposal submissions are due by **5PM GMT on Sunday, August 31st**.
 
 InnerSource Commons presentations will be any topic that is related to the practice of InnerSource. Here are a few topic ideas, others are welcome:
 

data/news.yaml

@@ -1,4 +1,4 @@
-- content: "Don’t miss your chance to speak at InnerSource Summit 2025! November 13, 2025 | Yokohama • Berlin • New York | [The Call for Presenters is now open.](https://bit.ly/ISCSummit25CFP) | Submit by 5PM GMT on Monday, July 15."
+- content: "Don’t miss your chance to speak at InnerSource Summit 2025! November 13, 2025 | Yokohama • Berlin • New York | [The Call for Presenters is now open.](https://bit.ly/ISCSummit25CFP) | Submit by 5PM GMT on Sunday, August 31."
   active: true
   type: "primary"