Add GitHub Actions CI

.github/workflows/ci.yaml

@@ -0,0 +1,37 @@
+---
+# vim: fileencoding=UTF-8:expandtab:autoindent:ts=2:sts=2:sw=2:filetype=yaml
+# yaml-language-server: $schema=https://json.schemastore.org/github-workflow
+name: CI
+
+# Controls when the action will run. Workflow runs when manually triggered
+# using the UI or API.
+'on':
+  push:
+    branches:
+      - '*'
+  pull_request:
+
+jobs:
+  test:
+    runs-on: 'ubuntu-latest'
+
+    steps:
+      - name: Check out tmpl.vim
+        uses: actions/checkout@v3
+        with:
+          path: tmpl.vim
+
+      - name: Fetch vader
+        uses: actions/checkout@v3
+        with:
+          repository: junegunn/vader.vim
+          path: vader.vim
+
+      - name: Install dependencies
+        run: sudo apt install -y neovim vim-nox
+
+      - name: Test with vim
+        run: VIM_BIN=vim ./tmpl.vim/tests/run_tests.sh
+
+      - name: Test with neovim
+        run: VIM_BIN=nvim ./tmpl.vim/tests/run_tests.sh