Add tests and GitHub Actions

Replace the Travis tests, which used a separate repo and no longer
ran, with tests in this repo. Each case in test/cases is indented as
a whole and should be unchanged, with optional syntax, fold and tag
checks. The cases are from the previous tests, plus script-setup.vue
for <script setup> keywords and a sync check in oneline.vim.

test/run.sh runs the cases with Vim in a pseudo terminal, as syntax in
Ex mode isn't the same, and Neovim headless.

test/cases/keyword.vue

@@ -0,0 +1,45 @@
+<script>
+  export default {
+    name: 'Home' as string,
+    data: function () {
+      return {
+        greeting: 'Hello'
+      };
+    },
+    data() {
+      return {
+        greeting: 'Hello'
+      };
+    },
+    computed: {
+      fullName() { // Computed Property returns a string
+        return `${this.user.firstName} ${this.user.lastName}`
+      }
+    },
+    mounted() { // The mounted hook returns nothing
+      ...
+    }
+  };
+</script>
+
+<script lang="ts">
+  import Vue from 'vue'
+  import { User } from '@/types'
+
+  export default Vue.extend({
+    name: 'Home' as string,
+    data() {
+      return {
+        user: {} as User
+      }
+    },
+    computed: {
+      fullName(): string { // Computed Property returns a string
+        return `${this.user.firstName} ${this.user.lastName}`
+      }
+    },
+    mounted(): void { // The mounted hook returns nothing
+      ...
+    }
+  })
+</script>