build(deps): Bump actions/download-artifact from 4 to 8

Bumps [actions/download-artifact](https://github.com/actions/download-artifact) from 4 to 8.
- [Release notes](https://github.com/actions/download-artifact/releases)
- [Commits](actions/download-artifact@v4...v8)

---
updated-dependencies:
- dependency-name: actions/download-artifact
  dependency-version: '8'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

.github/workflows/checks.yml

@@ -115,7 +115,7 @@ jobs:
       pull-requests: write
     steps:
       - name: Download build artifacts
-        uses: actions/download-artifact@v4
+        uses: actions/download-artifact@v8
         with:
           name: buckaroo-build
           path: artifacts
@@ -190,7 +190,7 @@ jobs:
           python-version: "3.13"
           prune-cache: false
       - name: Download build artifacts
-        uses: actions/download-artifact@v4
+        uses: actions/download-artifact@v8
         with:
           name: buckaroo-build
       - name: Install wheel with MCP extras
@@ -232,7 +232,7 @@ jobs:
           python-version: "3.13"
           prune-cache: false
       - name: Download build artifacts
-        uses: actions/download-artifact@v4
+        uses: actions/download-artifact@v8
         with:
           name: buckaroo-build
       - name: Smoke test — base install
@@ -387,7 +387,7 @@ jobs:
         working-directory: packages
         run: pnpm install --frozen-lockfile
       - name: Download build artifacts
-        uses: actions/download-artifact@v4
+        uses: actions/download-artifact@v8
         with:
           name: buckaroo-build
       - name: Cache Playwright browsers
@@ -533,7 +533,7 @@ jobs:
         working-directory: packages
         run: pnpm install --frozen-lockfile
       - name: Download build artifacts
-        uses: actions/download-artifact@v4
+        uses: actions/download-artifact@v8
         with:
           name: buckaroo-build
       - name: Cache Playwright browsers
@@ -570,7 +570,7 @@ jobs:
         working-directory: packages
         run: pnpm install --frozen-lockfile
       - name: Download build artifacts
-        uses: actions/download-artifact@v4
+        uses: actions/download-artifact@v8
         with:
           name: buckaroo-build
       - name: Install the project
@@ -609,7 +609,7 @@ jobs:
         working-directory: packages
         run: pnpm install --frozen-lockfile
       - name: Download build artifacts
-        uses: actions/download-artifact@v4
+        uses: actions/download-artifact@v8
         with:
           name: buckaroo-build
       - name: Install the project
@@ -682,7 +682,7 @@ jobs:
         working-directory: packages
         run: pnpm install --frozen-lockfile
       - name: Download build artifacts
-        uses: actions/download-artifact@v4
+        uses: actions/download-artifact@v8
         with:
           name: buckaroo-build
       - name: Install the project