Fix the Doc of alpha in mobilenet_v3 (#21563)

* Fix the Doc of `alpha` in `mobilenet_v3`

* Update keras/src/applications/mobilenet_v3.py

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

* Update mobilenet_v3.py

* Update mobilenet_v3.py

---------

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

Author: ILCSFNO

keras/src/applications/mobilenet_v3.py

@@ -91,6 +91,8 @@
     alpha: controls the width of the network. This is known as the
         depth multiplier in the MobileNetV3 paper, but the name is kept for
         consistency with MobileNetV1 in Keras.
+        When `weights` is `imagenet`, `alpha` can be one of `0.75` or `1.0`
+        for non-minimalistic models, and `1.0` for minimalistic models.
         - If `alpha < 1.0`, proportionally decreases the number
             of filters in each layer.
         - If `alpha > 1.0`, proportionally increases the number