Install dependeices before trying to use them in the Snyk github issue workflow

Signed-off-by: Harry Hogg <hhogg@spotify.com>

.github/workflows/snyk-github-issue-sync.yml

@@ -7,8 +7,42 @@ on:
 jobs:
   sync:
     runs-on: ubuntu-latest
+
+    strategy:
+      matrix:
+        node-version: [14.x]
+
     steps:
       - uses: actions/checkout@v2
+
+      # Beginning of yarn setup, keep in sync between all workflows, see ci.yml
+      - name: use node.js ${{ matrix.node-version }}
+        uses: actions/setup-node@v1
+        with:
+          node-version: ${{ matrix.node-version }}
+          registry-url: https://registry.npmjs.org/ # Needed for auth
+      - name: cache all node_modules
+        id: cache-modules
+        uses: actions/cache@v2
+        with:
+          path: '**/node_modules'
+          key: ${{ runner.os }}-v${{ matrix.node-version }}-node_modules-${{ hashFiles('yarn.lock', '**/package.json') }}
+      - name: find location of global yarn cache
+        id: yarn-cache
+        if: steps.cache-modules.outputs.cache-hit != 'true'
+        run: echo "::set-output name=dir::$(yarn cache dir)"
+      - name: cache global yarn cache
+        uses: actions/cache@v2
+        if: steps.cache-modules.outputs.cache-hit != 'true'
+        with:
+          path: ${{ steps.yarn-cache.outputs.dir }}
+          key: ${{ runner.os }}-yarn-${{ hashFiles('yarn.lock') }}
+          restore-keys: |
+            ${{ runner.os }}-yarn-
+      - name: yarn install
+        run: yarn install --frozen-lockfile
+      # End of yarn setup
+
       - name: Create Snyk report
         uses: snyk/actions/node@master
         continue-on-error: true # Snyk CLI exits with error when vulnerabilities are found