ci: Add workflow running vimscript linter

.github/workflows/vint.yml

@@ -0,0 +1,15 @@
+name: Vint
+on: [push]
+jobs:
+  vint:
+    name: vint
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+      - name: Set up Python
+        uses: actions/setup-python@v2
+      - name: Setup dependencies
+        run: pip install vim-vint
+      - name: Lint Vimscript
+        run: vint .