newsletter: Add section on CI

Author: gmta

src/content/newsletters/2025-06-30.mdx

@@ -64,6 +64,13 @@ will hook this up to the system's location services together with the necessary
 
 ![](/assets/img/newsletter-june-2025-geolocation.png)
 
+### CI: macOS and Windows
+
+In May, we've started using [Blacksmith's](https://blacksmith.sh/) action runners which already significantly reduced
+runtimes providing us with quicker iterations on both pull requests and benchmarks. In June, we started using our
+self-hosted macOS runner removing one of the last performance bottlenecks that we had for PRs. Additionally, we now
+support running CI for Windows on PRs which helps when reviewing them!
+
 ### Credits
 
 We'd like to thank everyone who contributed code this month: