Require uvloop >= 0.15.0

[ChihweiLHBird]

An issue (#2496) reported by @ancalita claims Sanic requires uvloop >= 0.15.0

During testing, the CI results (#2597) show that Sanic is broken with uvloop version less than 0.15.0

So, let's update the dependency requirement in setup.py to fix the issue.

uvloop PR: MagicStack/uvloop#334

[codecov]

Codecov Report

Base: 88.047% // Head: 88.047% // No change to project coverage 👍

Coverage data is based on head (ab78bda) compared to base (4422d0c).
Patch has no changes to coverable lines.

Additional details and impacted files

@@            Coverage Diff            @@
##              main     #2598   +/-   ##
=========================================
  Coverage   88.047%   88.047%           
=========================================
  Files           71        71           
  Lines         5338      5338           
  Branches       893       893           
=========================================
  Hits          4700      4700           
  Misses         461       461           
  Partials       177       177           

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