chore(ci): bump actions/checkout and artifact actions to v5

GitHub flagged checkout@v4 / upload-artifact@v4 / download-artifact@v4
as Node.js 20 actions, force-migrated to Node 24 on 2026-06-02. Bump
all nine references to v5 ahead of the deadline. The artifact steps are
v5-compatible: upload uses a unique matrix-target name and the download
step flattens subdirectories with find afterward.

.github/workflows/release.yml

@@ -32,7 +32,7 @@ jobs:
             os: windows-latest
 
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v5
 
       - uses: dtolnay/rust-toolchain@stable
         with:
@@ -98,7 +98,7 @@ jobs:
           fi
 
       - name: Upload artifact
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@v5
         with:
           name: ${{ matrix.target }}
           path: ${{ env.ASSET }}
@@ -110,7 +110,7 @@ jobs:
     permissions:
       contents: write
     steps:
-      - uses: actions/download-artifact@v4
+      - uses: actions/download-artifact@v5
         with:
           path: artifacts
 
@@ -142,7 +142,7 @@ jobs:
       contents: read
       packages: write
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v5
 
       - uses: docker/setup-qemu-action@v3
         with: