ci: up node to 18 as required

Author: glorat

.github/workflows/firebase-hosting-merge.yml

@@ -16,7 +16,7 @@ jobs:
       - uses: actions/checkout@v2
       - uses: actions/setup-node@v2
         with:
-          node-version: 16
+          node-version: 18
           cache: 'yarn'
           cache-dependency-path: yarn.lock
       - run: yarn install --frozen-lockfile
@@ -39,7 +39,7 @@ jobs:
       - uses: actions/checkout@v2
       - uses: actions/setup-node@v2
         with:
-          node-version: 16
+          node-version: 18
           cache: 'yarn'
           cache-dependency-path: yarn.lock
       - run: yarn install --frozen-lockfile