Install xindy as well

Author: tobiasdiez

.github/workflows/doc-build-pdf.yml

@@ -75,7 +75,7 @@ jobs:
         shell: bash -l {0}
         run: |
           sudo DEBIAN_FRONTEND=noninteractive sudo apt-get update
-          sudo DEBIAN_FRONTEND=noninteractive apt-get install $(build/bin/sage-get-system-packages debian texlive texlive_luatex free_fonts)
+          sudo DEBIAN_FRONTEND=noninteractive apt-get install $(build/bin/sage-get-system-packages debian texlive texlive_luatex free_fonts xindy)
           meson compile -C builddir doc-pdf
         env:
           SAGE_DOCBUILD_OPTS: "--include-tests-blocks"