chore: Move Tom Tan from maintainer to approver

[ThomsonTan]

Changes

• Move my entry from Maintainers to Approvers in README.md, keeping the Microsoft affiliation.

GitHub team membership needs a matching update.

For significant contributions please make sure you have completed the following items:

• CHANGELOG.md updated for non-trivial changes
• Unit tests have been added
• Changes in public API reviewed

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.65%. Comparing base (579486d) to head (0c71291).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4644      +/-   ##
==========================================
- Coverage   86.66%   86.65%   -0.00%     
==========================================
  Files         525      525              
  Lines       20481    20481              
==========================================
- Hits        17748    17746       -2     
- Misses       2733     2735       +2     

see 1 file with indirect coverage changes

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[lalitb]

LGTM. Thanks, @ThomsonTan , for all your contributions and support over the years! It’s been a pleasure working with you, and I’m glad you’ll stay involved as an approver.

[dbarker]

Thanks Tom!