Fix link to flags

Closes #44445
#44445

GitOrigin-RevId: 980bf9d
Change-Id: I7410a19af91a947553a58084c3babda98474427e
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/175701
Reviewed-by: Lasse R.H. Nielsen <[email protected]>

Author: mit-mit

docs/process/breaking-changes.md

@@ -35,7 +35,7 @@ abide by the following basic conditions:
 * Must access libraries via the public API (for example, must not reach into
   the internals of a package located in the `/src/` directory).
 
-* Must not rely on an [experiment flag](flags.md).
+* Must not rely on an [experiment flag](experimental-flags.md).
 
 * Must not circumvent clear restrictions documented in the public API
   documentation (for example, must not mixin a class clearly documented as