ci(workflows): update all actions to latest versions

- actions/setup-go: v5 → v6 (Go 1.25+ support)
- actions/upload-artifact: v4 → v6 (immutable artifacts)
- actions/download-artifact: v4 → v7 (attestations support)
- actions/github-script: v7 → v8 (Node 20)
- actions/checkout: standardized on v6

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.github/workflows/alpha-release.yml

@@ -29,7 +29,7 @@ jobs:
             platform: windows/amd64
     runs-on: ${{ matrix.os }}
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - name: Build
         uses: host-uk/build@v3
@@ -44,10 +44,10 @@ jobs:
     needs: build
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - name: Download artifacts
-        uses: actions/download-artifact@v4
+        uses: actions/download-artifact@v7
         with:
           path: dist
           merge-multiple: true

.github/workflows/coverage.yml

@@ -43,7 +43,7 @@ jobs:
           token: ${{ secrets.CODECOV_TOKEN }}
 
       - name: Upload coverage report
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@v6
         with:
           name: coverage-report
           path: coverage.txt

.github/workflows/pr-build.yml

@@ -29,7 +29,7 @@ jobs:
             platform: linux/amd64
     runs-on: ${{ matrix.os }}
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
         with:
           ref: ${{ github.event.pull_request.head.sha || github.sha }}
 
@@ -50,10 +50,10 @@ jobs:
       PR_NUM: ${{ github.event.pull_request.number || inputs.pr_number }}
       PR_SHA: ${{ github.event.pull_request.head.sha || github.sha }}
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - name: Download artifacts
-        uses: actions/download-artifact@v4
+        uses: actions/download-artifact@v7
         with:
           path: dist
           merge-multiple: true