Jetpack Social: Mastodon Social Preview Doesn't Resize Image Appropriately

### Impacted plugin

Social

### Quick summary

When previewing a social media post, the Mastodon preview doesn't properly resize the image:

### Steps to reproduce

1. Add a large Featured Image (my test image was 2104 x 1184)
2. Select Mastodon as a sharing destination
3. Access the preview function and observe that the image isn't properly resized in the Mastodon preview

### Site owner impact

Between 20% and 60% of the total website/platform users

### Severity

Minor

### What other impact(s) does this issue have?

No revenue impact

### If a workaround is available, please outline it here.

_No response_

### Platform (Simple and/or Atomic)

Self-hosted

The Jetpack Social Mastodon preview is the only entry point named; no source file or test is identified. Start by reproducing the issue with a large Featured Image and compare the Mastodon preview with the expected image sizing. Done means the preview resizes the image appropriately without affecting other sharing destinations.

Written by the indexing model from the issue text.