[css-anchor-position-1] Update changes list

Author: fantasai

css-anchor-position-1/Overview.bs

@@ -2635,5 +2635,7 @@ Significant changes since the <a href="https://www.w3.org/TR/2025/WD-css-anchor-
 	(<a href="https://github.com/w3c/csswg-drafts/issues/12869">Issue 12869</a>)
 * Add 'clip-path' to the list of clipping effects considered for ''anchors-visible''.
 	(<a href="https://github.com/w3c/csswg-drafts/issues/12732">Issue 12732</a>)
+* Fix error where base styles were accidentally left out of the [=position options list=].
+	(<a href="https://github.com/w3c/csswg-drafts/issues/12890">Issue 12890</a>)
 
 See also <a href="https://www.w3.org/TR/2025/WD-css-anchor-position-1-20251007/#changes">Previous Changes</a>.