adds cfp link to blog post (#303)

### Description

Adds CFP link to blog post ([using my
brain](#302) this
time compared to the last PR)
 
### Issues Resolved

n/a

### Check List
- [x] Commits are signed per the DCO using `--signoff`

By submitting this pull request, I confirm that my contribution is made
under the terms of the BSD-3-Clause License.

Signed-off-by: Kyle J. Davis <[email protected]>

Author: stockholmux

content/blog/2025-07-10-keyspace-save-the-date.md

@@ -19,4 +19,7 @@ Breakfast, lunch, happy hour, and exclusive Valkey swag is included.
 Keyspace is being held in conjunction with the [Linux Foundation Open Source Summit Europe](https://events.linuxfoundation.org/open-source-summit-europe/) at the [RAI Amsterdam Convention Centre](https://www.rai.nl/en).
 Tickets for Open Source Summit are not required to attend Keyspace.
 
+**Want to share _your_ Valkey story?** [Submit your talk by July 24](https://sessionize.com/keyspace/)!
+
+
 Tickets available soon.