DOC: re-word API change note

Co-authored-by: Tim Hoffmann <2836374+timhoffm@users.noreply.github.com>

Author: tacaswell

doc/api/next_api_changes/behavior/28437-CH.rst

@@ -1,15 +1,8 @@
-*alpha* parameter handling in _ImageBase._make_image
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+*alpha* parameter handling on images
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-This PR expands and clarifies code logic in _ImageBase._make_image
-related to the *alpha* parameter, and ensures that `~.Axes.imshow`
-exhibits the following behavior:
+When passing and array to `imshow(..., alpha=...)`, the parameter was silently ignored
+if the image data was a RGB or RBGA image or if `rcParams['interpolation_state']`
+resolved to "rbga".
 
-1. When the image does not have alpha channel:
-- *alpha* not specified: default to 1.0.
-- scalar *alpha*: broadcast.
-- array *alpha*: concatenate.
-2. When the image has an alpha channel:
-- *alpha* not specified: nothings needs to be done.
-- scalar *alpha*: multiply the alpha channel with user-specified scalar.
-- array *alpha*: replace the alpha channel with user-specified array.
+This is now fixed, and the alpha array overwrites any previous transparency information.