ci: Use Node 18 and upgrade actions (#1202)

Deals with this warning from GitHub Actions:

> Node.js 16 actions are deprecated. Please update the following actions
to use Node.js 20: actions/checkout@v2, actions/setup-node@v1,
actions/cache@v2.

Author: seb-cr

.github/workflows/main.yml

@@ -8,14 +8,14 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
 
-      - uses: actions/setup-node@v1
+      - uses: actions/setup-node@v4
         with:
-          node-version: 14
+          node-version: 18
 
       - name: Restore cache
-        uses: actions/cache@v2
+        uses: actions/cache@v4
         with:
           path: '**/node_modules'
           key: ${{ runner.os }}-modules-${{ hashFiles('**/yarn.lock') }}
@@ -31,14 +31,14 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
 
-      - uses: actions/setup-node@v1
+      - uses: actions/setup-node@v4
         with:
-          node-version: 14
+          node-version: 18
 
       - name: Restore cache
-        uses: actions/cache@v2
+        uses: actions/cache@v4
         with:
           path: '**/node_modules'
           key: ${{ runner.os }}-modules-${{ hashFiles('**/yarn.lock') }}
@@ -54,14 +54,14 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
 
-      - uses: actions/setup-node@v1
+      - uses: actions/setup-node@v4
         with:
-          node-version: 14
+          node-version: 18
 
       - name: Restore cache
-        uses: actions/cache@v2
+        uses: actions/cache@v4
         with:
           path: '**/node_modules'
           key: ${{ runner.os }}-modules-${{ hashFiles('**/yarn.lock') }}
@@ -77,10 +77,10 @@ jobs:
     if: github.ref == 'refs/heads/master' || github.ref == 'refs/heads/beta'
     steps:
       - name: Checkout
-        uses: actions/checkout@v2
+        uses: actions/checkout@v4
 
       - name: Restore cache
-        uses: actions/cache@v2
+        uses: actions/cache@v4
         with:
           path: '**/node_modules'
           key: ${{ runner.os }}-modules-${{ hashFiles('**/yarn.lock') }}