Fix icon vertical alignment in alert component

[lmac-1]

Description

This PR fixes vertical alignment for the sandbox banners on settings page. See screenshots on #4730 for before.

Closes #4730

Validation steps

1. Open a sandbox of a project
2. Go to "Settings"
3. Each settings panel should have an alert message - make sure that the vertical alignment looks correct. The change is subtle.
4. Also, try to merge the sandbox and check the icon - it should be aligned to the top header rather than in the middle

Additional notes for the reviewer

1. (Is there anything else the reviewer should know or look out for?)

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[github-actions]

Security Review ✅

• S0 (project scoping): N/A, change is purely CSS class adjustments in lib/lightning_web/live/components/common.ex with no data access.
• S1 (authorization): N/A, no new web-layer actions or handlers introduced.
• S2 (audit trail): N/A, no writes to configuration resources.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.3%. Comparing base (6331486) to head (547e500).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #4823     +/-   ##
=======================================
- Coverage   90.3%   90.3%   -0.0%     
=======================================
  Files        442     442             
  Lines      22545   22546      +1     
=======================================
  Hits       20350   20350             
- Misses      2195    2196      +1     

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[lmac-1]

Kicking off tests again because looks like tests failed (don't think it's related to my changes as they are just frontend)

[lmac-1]

They passed, yay!