Updated GitHub CI: Added Linux build and unit test

Author: orchetect

.github/workflows/build.yml

@@ -176,3 +176,13 @@ jobs:
     - name: Unit Tests
       if: steps.destnameprep.outcome != 'failure'
       run: xcodebuild test -workspace ".swiftpm/xcode/package.xcworkspace" -scheme "$SCHEME" -destination "platform=watchOS Simulator,name=$DESTNAME" | xcbeautify --renderer github-actions && exit ${PIPESTATUS[0]}
+
+  linux:
+    name: linux
+    runs-on: ubuntu-latests
+    steps:
+    - uses: actions/checkout@main
+    - name: Build
+      run: swift build
+    - name: Unit Tests
+      run: swift test