ci: upgrade actions to Node.js 24-compatible versions

Node.js 20 actions are deprecated and will be forced to Node.js 24
starting June 2, 2026. Bump to versions that ship Node.js 24 runtimes:

  actions/checkout        v4 → v6
  actions/setup-go        v5 → v6
  golangci-lint-action    v7 → v9
  actions/upload-artifact v4 → v6
  actions/download-artifact v4 → v8

.github/workflows/release.yml

@@ -32,10 +32,10 @@ jobs:
             binary: erupe-ce.exe
 
     steps:
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@v6
 
     - name: Set up Go
-      uses: actions/setup-go@v5
+      uses: actions/setup-go@v6
       with:
         go-version: '1.25'
 
@@ -56,7 +56,7 @@ jobs:
         cd staging && zip -r ../erupe-${{ matrix.os_name }}.zip .
 
     - name: Upload build artifact
-      uses: actions/upload-artifact@v4
+      uses: actions/upload-artifact@v6
       with:
         name: ${{ matrix.os_name }}
         path: erupe-${{ matrix.os_name }}.zip
@@ -68,7 +68,7 @@ jobs:
 
     steps:
     - name: Checkout repository
-      uses: actions/checkout@v4
+      uses: actions/checkout@v6
 
     - name: Log in to the Container registry
       uses: docker/login-action@v3
@@ -108,10 +108,10 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@v6
 
     - name: Download all artifacts
-      uses: actions/download-artifact@v4
+      uses: actions/download-artifact@v8
       with:
         path: artifacts
         pattern: '*-amd64'