CI: use caching for JavaScript workflows (#3167)

* build: use actions/setup-node@v2 with caching

This attempts to use the "cache: yarn" directive, as described in https://github.com/actions/setup-node/blob/main/docs/advanced-usage.md#caching-packages-dependencies

* build: use cache: yarn in js-lint workflow

* fix: checkout before using yarn.lock in js-lint

The issue came up when trying to use a yarn.lock, when there was none.

/usr/local/bin/yarn cache dir
/home/runner/.cache/yarn/v6
Error: Dependencies lock file is not found in /home/runner/work/webpacker/webpacker. Supported file patterns: yarn.lock

Author: olleolleolle

.github/workflows/jest.yml

@@ -15,25 +15,14 @@ jobs:
     steps:
       - uses: actions/checkout@v2
       - name: Use Node.js ${{ matrix.node }}
-        uses: actions/setup-node@v1
+        uses: actions/setup-node@v2
         with:
           node-version: ${{ matrix.node }}
+          cache: yarn
 
       - name: Install yarn maybe
         run: which yarn || npm install -g yarn
 
-      - name: Get yarn cache directory path
-        id: yarn-cache-dir-path
-        run: echo "::set-output name=dir::$(yarn cache dir)"
-
-      - uses: actions/cache@v2
-        id: yarn-cache # use this to check for `cache-hit` (`steps.yarn-cache.outputs.cache-hit != 'true'`)
-        with:
-          path: ${{ steps.yarn-cache-dir-path.outputs.dir }}
-          key: ${{ runner.os }}-${{ matrix.node }}-yarn-${{ hashFiles('**/yarn.lock') }}
-          restore-keys: |
-            ${{ runner.os }}-${{ matrix.node }}-yarn-
-
       - name: Install dependencies
         run: yarn --frozen-lockfile
 

.github/workflows/js-lint.yml

@@ -14,27 +14,16 @@ jobs:
     runs-on: ${{ matrix.os }}
 
     steps:
+      - uses: actions/checkout@v2
       - name: Use Node.js ${{ matrix.node }}
-        uses: actions/setup-node@v1
+        uses: actions/setup-node@v2
         with:
           node-version: ${{ matrix.node }}
+          cache: yarn
 
       - name: Install yarn maybe
         run: which yarn || npm install -g yarn
 
-      - uses: actions/checkout@v2
-      - name: Get yarn cache directory path
-        id: yarn-cache-dir-path
-        run: echo "::set-output name=dir::$(yarn cache dir)"
-
-      - uses: actions/cache@v2
-        id: yarn-cache # use this to check for `cache-hit` (`steps.yarn-cache.outputs.cache-hit != 'true'`)
-        with:
-          path: ${{ steps.yarn-cache-dir-path.outputs.dir }}
-          key: ${{ runner.os }}-yarn-${{ hashFiles('**/yarn.lock') }}
-          restore-keys: |
-            ${{ runner.os }}-yarn-
-
       - name: Install dependencies
         run: yarn --frozen-lockfile