Update CHANGELOG to reflect breaking change #36765

 * This change is being enforced server-side on pub.dev.
 * This CHANGELOG entry is added for compliance with
   `docs/process/breaking-changes.md`.

Change-Id: I9e10c4f224e084db6b6c78d637bb01a2a59565b3
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/108409
Reviewed-by: Sigurd Meldgaard <[email protected]>
Commit-Queue: Sigurd Meldgaard <[email protected]>
Auto-Submit: Jonas Jensen <[email protected]>

Author: jonasfj

CHANGELOG.md

@@ -117,6 +117,9 @@
 #### Pub
 
  * Clean-up invalid git repositories in cache when fetching from git.
+ * **Breaking change**  [#36765](https://github.com/dart-lang/sdk/issues/36765):
+   Packages published to [pub.dev](https://pub.dev) can no longer contain git
+   dependencies. These packages will be rejected by the server.
 
 #### Linter