fix: Make message section on re-designed signature pages scrollable

[jpuri]

Description

As scroll to message section on re-designed signature request pages.

Related issues

Fixes: https://github.com/MetaMask/MetaMask-planning/issues/3915

Manual testing steps

1. Enable re-designs locally
2. Submit signature request
3. Check scroll in expanded message section

Screenshots/Recordings

Screen.Recording.2025-01-15.at.3.39.14.PM.mov

Pre-merge author checklist

• I’ve followed MetaMask Contributor Docs and MetaMask Mobile Coding Standards.
• I've completed the PR template to the best of my ability
• I’ve included tests if applicable
• I’ve documented my code using JSDoc format if applicable
• I’ve applied the right labels on the PR (see labeling guidelines). Not required for external contributors.

Pre-merge reviewer checklist

• I've manually tested the PR (e.g. pull and build branch, run the app, test code being changed).
• I confirm that this PR addresses all acceptance criteria described in the ticket it closes and includes the necessary testing evidence such as recordings and or screenshots.

[github-actions]

CLA Signature Action: All authors have signed the CLA. You may need to manually re-run the blocking PR check if it doesn't pass in a few minutes.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 59.83%. Comparing base (6b68dd7) to head (b0cf73c).
Report is 18 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #12998      +/-   ##
==========================================
+ Coverage   59.72%   59.83%   +0.10%     
==========================================
  Files        1865     1873       +8     
  Lines       42011    42121     +110     
  Branches     5458     5473      +15     
==========================================
+ Hits        25093    25201     +108     
+ Misses      15239    15238       -1     
- Partials     1679     1682       +3     

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[github-actions]

Bitrise

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Commit hash: b0cf73c
Build link: https://app.bitrise.io/app/be69d4368ee7e86d/pipelines/13225477-f83c-47b8-b82d-547c75b24f21

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