Update AGENTS.md

Co-authored-by: Andrew Murray <3112309+radarhere@users.noreply.github.com>

Author: aclark4life

AGENTS.md

@@ -99,4 +99,4 @@ Use fully qualified exception names: `Image.DecompressionBombError` and
 `Image.DecompressionBombWarning`, not the bare class names.
 
 Do not embed specific numeric values for thresholds like `MAX_IMAGE_PIXELS` —
-they change across releases. Reference the named constant instead.
+they may be changed by the user at runtime. Reference the named constant instead.