add Github Action to run the tests

CircleCI doesn't seem to be running on the repository. This also makes
it easy for people who fork the repo to run the CI since it is enabled
by default on all the repositories.

.circleci/config.yml

@@ -1,18 +0,0 @@
-version: 2
-
-jobs:
-  nix:
-    docker:
-      - image: nixos/nix:latest
-    working_directory: ~/NixGL
-    steps:
-      - checkout
-      - run:
-          name: Build all wrapper (with default version for nvidia)
-          command: nix-build ./all.nix
-
-workflows:
-  version: 2
-  nix_stack:
-    jobs:
-      - nix

.github/workflows/test.yml

@@ -0,0 +1,13 @@
+name: 'Test'
+
+on: [ push, pull_request ]
+
+jobs:
+  test:
+    name: 'Test'
+    runs-on: ubuntu-18.04
+    steps:
+    - uses: actions/checkout@v2
+    - uses: cachix/install-nix-action@v8
+    - run: nix-build all.nix
+