Switch to g++-12, g++-13 not available in jammy repos.

docker/Dockerfile.ci

@@ -69,7 +69,7 @@ RUN if [ "${BUILD_SYCL_MODULE}" = "ON" ]; then \
 
 # Dependencies: basic and python-build
 # gcc-11 causes a seg fault in tensormap when built in Release mode. Upgrade to
-# gcc-13 instead.
+# gcc-12 instead.
 RUN apt-get update && apt-get install -y \
     git  \
     wget \
@@ -90,8 +90,8 @@ RUN apt-get update && apt-get install -y \
     libffi-dev \
     liblzma-dev \
  && if c++ --version | grep -F ' 11.' ; then \
-        apt-get install -y g++-13 \
-        && update-alternatives --install /usr/bin/c++ c++ /usr/bin/g++-13 100 \
+        apt-get install -y g++-12 \
+        && update-alternatives --install /usr/bin/c++ c++ /usr/bin/g++-12 100 \
         && c++ --version; \
     fi \
  && rm -rf /var/lib/apt/lists/*