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

- Add ca-certificates to the Dockerfile apt install. This was
  accidentally removed as a transitive dependency when python3-pip was
  removed in a prior commit. Without it, git inside the container fails
  with 'server certificate verification failed'.

- Downgrade sphinxcontrib-phpdomain from 0.15.2 to 0.13.2. The 0.15.x
  versions (Requires-Python >=3.13.5) are only installable from the
  GARM runner pip cache; on ephemeral GitHub-hosted runners pip resolves
  compatibility against the Ubuntu 24.04 system Python 3.12 rather than
  the actions/setup-python 3.13 install, causing failure. 0.13.2 is the
  latest version reliably available on public PyPI from any runner.

Agent-Logs-Url: https://github.com/nextcloud/documentation/sessions/1a438572-858a-428c-b663-e9791fbe23b2

Co-authored-by: skjnldsv <14975046+skjnldsv@users.noreply.github.com>

Author: Copilot

.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 \

requirements.txt

@@ -29,7 +29,7 @@ sphinxcontrib-jquery==4.1
 sphinxcontrib-jsmath==1.0.1
 sphinxcontrib-mermaid==2.0.1
 sphinx-notfound-page==1.1.0
-sphinxcontrib-phpdomain==0.15.2
+sphinxcontrib-phpdomain==0.13.2
 sphinxcontrib-qthelp==2.0.0
 sphinxcontrib-serializinghtml==2.0.0
 sphinx-toolbox==4.1.2