Add GHA-based testing (#4)

* Add GHA-based testing

* Switch `StateSelection` to HTTPS URL, rather than git.

* Disable coverage

.github/workflows/runtests.yml

@@ -0,0 +1,34 @@
+name: Run tests
+
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+
+# needed to allow julia-actions/cache to delete old caches that it has created
+permissions:
+  actions: write
+  contents: read
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        # Eventually, we'll put '1' here as well
+        julia-version: ['nightly']
+
+    steps:
+      - uses: actions/checkout@v4
+      - uses: julia-actions/setup-julia@v1
+        with:
+          version: ${{ matrix.julia-version }}
+          arch: x64
+      - uses: julia-actions/cache@v1
+      - uses: julia-actions/julia-buildpkg@v1
+      - uses: julia-actions/julia-runtest@v1
+        with:
+          coverage: false
+        # with:
+        #   annotate: true