CI: Update token-group and token-metadata JS jobs to Node 20 (solana-labs#7365)

#### Problem

The token-group and token-metadata JS packages now require at least Node
v19, but the specific workflows only use v16.

#### Summary of changes

Update the CI job to v20.

Author: joncinque

.github/workflows/pull-request-libraries.yml

@@ -66,7 +66,7 @@ jobs:
   js-test:
     runs-on: ubuntu-latest
     env:
-      NODE_VERSION: 20.5
+      NODE_VERSION: 20.x
     steps:
       - uses: actions/checkout@v4
       - name: Use Node.js ${{ env.NODE_VERSION }}

.github/workflows/pull-request-token-group.yml

@@ -74,7 +74,7 @@ jobs:
   js-test:
     runs-on: ubuntu-latest
     env:
-      NODE_VERSION: 16.x
+      NODE_VERSION: 20.x
     steps:
       - uses: actions/checkout@v4
       - name: Use Node.js ${{ env.NODE_VERSION }}

.github/workflows/pull-request-token-metadata.yml

@@ -75,7 +75,7 @@ jobs:
   js-test:
     runs-on: ubuntu-latest
     env:
-      NODE_VERSION: 16.x
+      NODE_VERSION: 20.x
     steps:
       - uses: actions/checkout@v4
       - name: Use Node.js ${{ env.NODE_VERSION }}