Merge pull request #14507 from nextcloud/backport/14506/master

[master] fix: add ca-certificates to Dockerfile and downgrade sphinxcontrib-phpdomain

Author: skjnldsv

.docker/sphinx-latex/Dockerfile

@@ -8,6 +8,7 @@ ENV DEBIAN_FRONTEND=noninteractive
 
 RUN apt-get update \
   && apt-get install -y --no-install-recommends \
+    ca-certificates \
     curl \
     git \
     lsb-release \