chore(deps): bump actions/upload-artifact from 5 to 6

Bumps [actions/upload-artifact](https://github.com/actions/upload-artifact) from 5 to 6.
- [Release notes](https://github.com/actions/upload-artifact/releases)
- [Commits](https://github.com/actions/upload-artifact/compare/v5...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>

.github/workflows/ci.yml

@@ -174,7 +174,7 @@ jobs:
         run: cargo build -p deltachat_ffi
 
       - name: Upload C library
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v6
         with:
           name: ${{ matrix.os }}-libdeltachat.a
           path: target/debug/libdeltachat.a
@@ -200,7 +200,7 @@ jobs:
         run: cargo build -p deltachat-rpc-server
 
       - name: Upload deltachat-rpc-server
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v6
         with:
           name: ${{ matrix.os }}-deltachat-rpc-server
           path: ${{ matrix.os == 'windows-latest' && 'target/debug/deltachat-rpc-server.exe' || 'target/debug/deltachat-rpc-server' }}