Fix minimum swift-nio version to use async/await FileIO APIs.

[sidepelican]

2.0.0-beta.2 uses async/await FileIO APIs in NIO.

Package.swift points to 2.62.0 as the minimum version, but this API was introduced in 2.63.0.
INFO: https://github.com/apple/swift-nio/releases/tag/2.63.0

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 83.89%. Comparing base (e78cde7) to head (cc29978).
Report is 19 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #414      +/-   ##
==========================================
- Coverage   84.86%   83.89%   -0.98%     
==========================================
  Files          98      100       +2     
  Lines        5320     4135    -1185     
==========================================
- Hits         4515     3469    -1046     
+ Misses        805      666     -139     

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[adam-fowler]

Thank you