Fix warning CA1062#AsyncFallbackPolicy

[Zombach]

Pull Request

The issue or feature being addressed

#2215

Details on the issue fix or feature implementation

• Suppress CA1062 in src/Polly/Fallback/AsyncFallbackPolicy.cs or fix the warning

Confirm the following

• I started this PR by branching from the head of the default branch
• I have targeted the PR to merge into the default branch
• I have included unit tests for the issue/feature

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.00%. Comparing base (72331dc) to head (fa3da38).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2233   +/-   ##
=======================================
  Coverage   84.00%   84.00%           
=======================================
  Files         313      313           
  Lines        7227     7229    +2     
  Branches     1078     1079    +1     
=======================================
+ Hits         6071     6073    +2     
  Misses        785      785           
  Partials      371      371           

Flag	Coverage Δ
linux	84.00% <100.00%> (+<0.01%)	⬆️
macos	84.00% <100.00%> (+<0.01%)	⬆️
windows	84.00% <100.00%> (+<0.01%)	⬆️

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