Update contrast agnostic model to v2.4 (now improved for lumbar t2w +…

… PSIR/STIR images) (#4510)

## Description

The differences between v2.3 and 2.4 are mainly focused on lumbar
t2w and PSIR/STIR images: [diff of release
body](https://www.diffchecker.com/WSVngW4s/)

This should be a good test for our "keep models up to date" code. If
everything works correctly, you should be able to check out this branch,
then run the `sct_deepseg -task` command, and the code will
automatically verify the version of the model and download the newest
version if your local version is out of date.

## Linked issues
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Fixes #4509.

spinalcordtoolbox/deepseg/models.py

@@ -139,7 +139,7 @@
     #       - Binarization is applied within SCT code
     "model_seg_sc_contrast_agnostic_softseg_monai": {
         "url": [
-            "https://github.com/sct-pipeline/contrast-agnostic-softseg-spinalcord/releases/download/v2.3/model_soft_bin_20240410-1136.zip"
+            "https://github.com/sct-pipeline/contrast-agnostic-softseg-spinalcord/releases/download/v2.4/model_soft_bin_20240425-170840.zip"
         ],
         "description": "Spinal cord segmentation agnostic to MRI contrasts using MONAI-based nnUNet model",
         "contrasts": ["any"],