Added SPM build action (#4576)

.github/workflows/swift.yml

@@ -53,3 +53,13 @@ jobs:
       - uses: actions/checkout@v2
       - name: iOS - ${{ matrix.destination }}
         run: set -o pipefail && env NSUnbufferedIO=YES xcodebuild -workspace "Charts.xcworkspace" -scheme "ChartsDemo-iOS" -destination "${{ matrix.destination }}" clean build | xcpretty
+
+  spm:
+    name: Test with SPM
+    runs-on: macOS-latest
+    env:
+      DEVELOPER_DIR: /Applications/Xcode_12.4.app/Contents/Developer
+    steps:
+      - uses: actions/checkout@v2
+      - name: SPM Test
+        run: swift build -c debug