[release] v9.3.1

[brijeshb42]

Hotfix release for the exit-transitions regression.

Cherry-picked from master onto release/9.3.1 (cut at v9.3.0):

• [transitions] Prevent exit transitions from getting stuck ([transitions] Prevent exit transitions from getting stuck #48881)
• [test][pagination] Add more unit tests ([test][pagination] Add more unit tests #48927)
• [blog] Clarify early bird renewal discount scope ([blog] Clarify early bird renewal discount scope #48906)

Plus version bumps (@mui/material, @mui/core-downloads-tracker → 9.3.1) and the changelog.

[brijeshb42]

Closing — this was a dry run of the hotfix flow.