Add apt install fontconfig for doc-links in CI too

.github/workflows/ci.yml

@@ -94,6 +94,8 @@ jobs:
     name: Intra-doc links
     runs-on: ubuntu-latest
     steps:
+      - name: Install dependencies (needed for yeslogic-fontconfig-sys crate)
+        if: matrix.os == 'ubuntu-latest'
       - uses: actions/checkout@v4
       - run: cargo fetch
       # Requires #![deny(rustdoc::broken_intra_doc_links)] in crates.