Create initial Github Actions test workflow

Author: Matej Cotman

.github/workflows/test.yml

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+name: Test
+
+# Controls when the workflow will run
+on:
+  # Triggers the workflow on push or pull request events but only for the master branch
+  push:
+    branches: [ tests ]
+  pull_request:
+    branches: [ tests ]
+
+  # Allows you to run this workflow manually from the Actions tab
+  workflow_dispatch:
+
+# A workflow run is made up of one or more jobs that can run sequentially or in parallel
+jobs:
+    
+  # This workflow contains a single job called "tests"
+  tests:
+    # The type of runner that the job will run on
+    runs-on: ubuntu-latest
+
+    # Steps represent a sequence of tasks that will be executed as part of the job
+    steps:
+      # Checks-out your repository under $GITHUB_WORKSPACE, so your job can access it
+      - uses: actions/checkout@v2
+
+      - uses: cachix/install-nix-action@v13
+        with:
+          nix_path: nixpkgs=channel:nixos-unstable
+
+      - run: nix-shell --argstr cmd "invoke test --in-nix" --argstr python python37 --argstr rfVersion 3.0.4