Fix CI build for iOS wrapper

[Patrik-Stas]

Github Actions started by default using xcode 12 which causes us some issue when building for ios https://stackoverflow.com/questions/63607158/xcode-12-building-for-ios-simulator-but-linking-in-object-file-built-for-ios

Solved in this PR by switching back to xcode 11

Signed-off-by: Patrik Stas patrik.stas@absa.africa

[codecov-io]

Codecov Report

Merging #177 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #177   +/-   ##
=======================================
  Coverage   51.11%   51.11%           
=======================================
  Files         151      151           
  Lines       22923    22923           
  Branches     6053     6053           
=======================================
  Hits        11716    11716           
  Misses       7600     7600           
  Partials     3607     3607           

Flag	Coverage Δ
unittests	51.11% <ø> (ø)

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