ci: bump actions/upload-artifact from 4 to 6

Bumps [actions/upload-artifact](https://github.com/actions/upload-artifact) from 4 to 6.
- [Release notes](https://github.com/actions/upload-artifact/releases)
- [Commits](actions/upload-artifact@v4...v6)

---
updated-dependencies:
- dependency-name: actions/upload-artifact
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

.github/workflows/ci.yml

@@ -53,7 +53,7 @@ jobs:
         run: pnpm run build
 
       - name: Upload build artifacts
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@v6
         with:
           name: build-artifacts
           path: |

.github/workflows/release.yml

@@ -69,7 +69,7 @@ jobs:
         working-directory: packages/vscode-extension
 
       - name: Upload VSCode extension artifact
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@v6
         with:
           name: vscode-extension
           path: packages/vscode-extension/*.vsix
@@ -100,7 +100,7 @@ jobs:
         working-directory: packages/cursor-extension
 
       - name: Upload Cursor extension artifact
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@v6
         with:
           name: cursor-extension
           path: packages/cursor-extension/*.vsix