Update Swift Concurrency availability to include macOS 10.15, iOS 13.0 etc

[adam-fowler]

No description provided.

[codecov]

Codecov Report

Base: 78.08% // Head: 78.08% // No change to project coverage 👍

Coverage data is based on head (01fac65) compared to base (3feb2ba).
Patch has no changes to coverable lines.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #140   +/-   ##
=======================================
  Coverage   78.08%   78.08%           
=======================================
  Files          72       72           
  Lines        3094     3094           
=======================================
  Hits         2416     2416           
  Misses        678      678           

Impacted Files	Coverage Δ
...ummingbird/AsyncAwaitSupport/AsyncMiddleware.swift	0.00% <ø> (ø)
...Hummingbird/AsyncAwaitSupport/AsyncResponder.swift	0.00% <ø> (ø)
...gbird/AsyncAwaitSupport/ConnectionPool+async.swift	0.00% <ø> (ø)
...bird/AsyncAwaitSupport/Request+Persist+async.swift	0.00% <ø> (ø)
...ingbird/AsyncAwaitSupport/RouteHandler+async.swift	0.00% <ø> (ø)
...s/Hummingbird/AsyncAwaitSupport/Router+async.swift	0.00% <ø> (ø)
Sources/Hummingbird/Router/RouterMethods.swift	97.50% <ø> (ø)
...irdFoundation/AsyncAwaitSupport/FileIO+async.swift	0.00% <ø> (ø)
Sources/HummingbirdFoundation/Files/FileIO.swift	86.73% <ø> (ø)
...s/HummingbirdJobs/AsyncAwaitSupport/AsyncJob.swift	0.00% <ø> (ø)
... and 1 more

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