fix(CI): move to Xcode 12 and use explicit iOS 14.0 version (#320)

* fix(CI): move to Xcode 12 and use explicit iOS 14.0 version

* Also use Xcode to build and test Libraries such as Backend or UI as
they need WidgetKit to be builded and tested now

* build(Scheme): add UITests Target to test UI

.github/workflows/xcodebuild.yml

@@ -8,24 +8,24 @@ jobs:
 
     steps:
     - uses: actions/checkout@v2
-        
+
     - name: Select Xcode
-      run: sudo xcode-select -switch /Applications/Xcode_12_beta.app
+      run: sudo xcode-select -switch /Applications/Xcode_12.app
 
     - name: Xcode version
       run: /usr/bin/xcodebuild -version
 
     - name: Xcode test backend
       run: |
-        cd ACHNBrowserUI/Packages/Backend/
-        swift test
+        cd ACHNBrowserUI/
+        xcodebuild clean test -scheme Backend -destination 'platform=iOS Simulator,name=iPhone 11,OS=14.0'
 
     - name: Xcode test UI
       run: |
-        cd ACHNBrowserUI/Packages/UI/
-        swift test
+        cd ACHNBrowserUI/
+        xcodebuild clean test -scheme UI -destination 'platform=iOS Simulator,name=iPhone 11,OS=14.0'
 
     - name: Xcode build iOS App
       run: |
         cd ACHNBrowserUI/
-        xcodebuild clean build -scheme ACHNBrowserUI -destination 'platform=iOS Simulator,name=iPhone 11,OS=14'
+        xcodebuild clean build -scheme ACHNBrowserUI -destination 'platform=iOS Simulator,name=iPhone 11,OS=14.0'

ACHNBrowserUI/Packages/UI/.swiftpm/xcode/xcshareddata/xcschemes/UI.xcscheme

@@ -28,6 +28,16 @@
       selectedLauncherIdentifier = "Xcode.DebuggerFoundation.Launcher.LLDB"
       shouldUseLaunchSchemeArgsEnv = "YES">
       <Testables>
+         <TestableReference
+            skipped = "NO">
+            <BuildableReference
+               BuildableIdentifier = "primary"
+               BlueprintIdentifier = "UITests"
+               BuildableName = "UITests"
+               BlueprintName = "UITests"
+               ReferencedContainer = "container:">
+            </BuildableReference>
+         </TestableReference>
       </Testables>
    </TestAction>
    <LaunchAction