fix: update GitHub Actions to Node.js 24-compatible versions (#30)

Bump actions/checkout from v4 to v6, actions/cache from v4 to v5, and
actions/setup-node from v4 to v6 to avoid the forced migration away from
Node.js 20 runners on June 2, 2026.

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: andeplane

.github/workflows/ci.yml

@@ -12,10 +12,10 @@ jobs:
     timeout-minutes: 60
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
 
       - name: Cache emsdk
-        uses: actions/cache@v4
+        uses: actions/cache@v5
         with:
           path: ~/emsdk
           key: emsdk-${{ runner.os }}-${{ hashFiles('emsdk_manifest.txt') }}
@@ -30,7 +30,7 @@ jobs:
           ./emsdk activate 3.1.51
 
       - name: Setup Node.js
-        uses: actions/setup-node@v4
+        uses: actions/setup-node@v6
         with:
           node-version: 20
           cache: 'npm'

.github/workflows/release.yml

@@ -15,7 +15,7 @@ jobs:
       id-token: write
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
         with:
           fetch-depth: 2
 
@@ -33,7 +33,7 @@ jobs:
           fi
 
       - name: Cache emsdk
-        uses: actions/cache@v4
+        uses: actions/cache@v5
         with:
           path: ~/emsdk
           key: emsdk-${{ runner.os }}-${{ hashFiles('emsdk_manifest.txt') }}
@@ -48,7 +48,7 @@ jobs:
           ./emsdk activate 3.1.51
 
       - name: Setup Node.js
-        uses: actions/setup-node@v4
+        uses: actions/setup-node@v6
         with:
           node-version: 20
           cache: npm