Update actions to versions running on Node20

As per
https://github.blog/changelog/2023-09-22-github-actions-transitioning-from-node-16-to-node-20/,
GitHub has started a deprecation process for the GitHub Actions that run on
Node16. We're updating Actions that use this version of Node to newer versions,
running on Node20.

.github/workflows/ci.yml

@@ -15,9 +15,9 @@ jobs:
     name: Build
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
 
-      - uses: actions/setup-node@v3
+      - uses: actions/setup-node@v4
         with:
           node-version: "16"
           cache: "yarn"
@@ -45,7 +45,7 @@ jobs:
           POSTHOG_API_KEY: ${{ secrets.MAINNET_POSTHOG_API_KEY }}
           POSTHOG_HOSTNAME_HTTP: ${{ secrets.MAINNET_POSTHOG_HOSTNAME_HTTP }}
 
-      - uses: actions/upload-artifact@v3
+      - uses: actions/upload-artifact@v4
         with:
           name: build
           path: public
@@ -56,9 +56,9 @@ jobs:
     if: github.event_name == 'pull_request'
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
 
-      - uses: actions/download-artifact@v3
+      - uses: actions/download-artifact@v4
 
       - name: Deploy PR to GCP
         uses: thesis/gcp-storage-bucket-action@v3.1.0
@@ -70,7 +70,7 @@ jobs:
           build-folder: build
 
       - name: Post preview URL to PR
-        uses: actions/github-script@v6
+        uses: actions/github-script@v7
         with:
           script: |
             github.rest.issues.createComment({
@@ -89,9 +89,9 @@ jobs:
       name: prod
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
 
-      - uses: actions/download-artifact@v3
+      - uses: actions/download-artifact@v4
 
       - name: Deploy build to GCP
         uses: thesis/gcp-storage-bucket-action@v3.1.0