Run tests on push with GitHub Actions (#692)

* Run tests on push with GitHub Actions

* Ensure sizes match those listed in README

* Fix two icons which were failing validation

.github/workflows/test.yml

@@ -0,0 +1,15 @@
+name: Run tests
+
+on:
+  [push]
+
+jobs:
+  test:
+
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v3
+      - uses: actions/setup-node@v3
+      - run: npm install
+      - run: npm test