ci: fix Babel 8 and Node.js 6 jobs

- Target ie11 in the Gruntfile so the fixture is transpiled regardless of
  preset-env's default targets, which differ between Babel 7 and 8 (Babel 8
  no longer lowers `class` by default, breaking the test assertion).
- Install with --ignore-engines so eslint's newer Node.js requirement does
  not abort dependency installation on Node.js 6 (eslint runs in its own job).
- Fix the matrix exclude to skip Node.js 6 + Babel 8 (Babel 8 needs Node 20+).

Author: nicolo-ribaudo

.github/workflows/test.yml

@@ -16,8 +16,8 @@ jobs:
         node: [6, 22, 24, 26]
         babel: [7, 8]
         exclude:
-          # Babel 8 requires Node.js 20+, so it cannot run on Node.js 8.
-          - node: 8
+          # Babel 8 requires Node.js 20+, so it cannot run on Node.js 6.
+          - node: 6
             babel: 8
     steps:
       - uses: actions/checkout@v4
@@ -28,7 +28,10 @@ jobs:
           node-version: ${{ matrix.node }}
 
       - name: Install dependencies (Babel 7)
-        run: yarn install --frozen-lockfile
+        # --ignore-engines: dev-only tools such as eslint declare a newer
+        # minimum Node.js version, but they are not executed in this job
+        # (linting runs in its own job), so installing them on Node.js 6 is fine.
+        run: yarn install --frozen-lockfile --ignore-engines
 
       - name: Upgrade dev dependencies to Babel 8
         if: matrix.babel == 8

Gruntfile.js

@@ -5,7 +5,10 @@ module.exports = function(grunt) {
       compile: {
         options: {
           sourceMap: true,
-          presets: ["@babel/preset-env"],
+          // Target an old environment so that the test fixture is actually
+          // transpiled (e.g. classes -> functions) regardless of the default
+          // targets, which differ between Babel 7 and Babel 8.
+          presets: [["@babel/preset-env", { targets: { ie: "11" } }]],
         },
         files: {
           "test/tmp/fixture-compiled.js": "test/fixtures/fixture.js",