Add CI as GH workflow

.ci.ston

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+SmalltalkCISpec {
+  #loading : [
+    SCIMetacelloLoadSpec {
+      #baseline : 'SpecBrick',
+      #directory : 'src',
+      #platforms : [ #pharo ]
+    }
+  ],
+  #testing: {
+    #include : {
+     #packages : [ 'Spec-Brick.*' ]
+    }
+  }
+}

.github/workflows/Tests.yml

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+on: [ push, pull_request, workflow_dispatch ]
+
+jobs:
+  test:
+    strategy:
+      # Default value means that a failure in one OS cancels all 
+      fail-fast: false
+      matrix:
+        smalltalk: [ Pharo64-9.0 ]
+        os: [ macos-latest, ubuntu-latest, windows-latest ]
+        ston: [ .ci.ston ]
+    runs-on: ${{ matrix.os }}
+    name: ${{ matrix.smalltalk }} on ${{ matrix.os }}
+    steps:
+      - uses: actions/checkout@v2
+      - name: Setup smalltalkCI
+        uses: hpi-swa/setup-smalltalkCI@v1
+        with:
+          smalltalk-image: ${{ matrix.smalltalk }}
+      - name: Load in New Image and Run Tests
+        run: smalltalkci -s ${{ matrix.smalltalk }} ${{ matrix.ston }}
+        shell: bash
+        timeout-minutes: 10