ci: Install a newer Python 3.10 for QtWebKit image

Starting with the upgrade to Hypothesis 6.103.4 we got hangs when pytest exits.
This is caused by:

https://github.com/HypothesisWorks/hypothesis/pull/4013

combined with:

https://github.com/python/cpython/issues/102126

which was fixed in Python 3.10.11, but the latest 3.10 packaged by Archlinux was
3.10.10.

Thus, we instead build a newer 3.10 from the AUR.
This bumps the build time up to about 20 minutes on my machine, which is
probably acceptable since those are nightly builds only anyways. We could
probably half that by disabling --enable-optimization, but that would be at the
cost of making the actual test runs (which run more often) slower.

Closes #8247

scripts/dev/ci/docker/Dockerfile.j2

@@ -36,11 +36,14 @@ RUN pacman -Su --noconfirm \
     libyaml \
     xorg-xdpyinfo
 
+RUN useradd user -u 1001 && \
+    mkdir /home/user && \
+    chown user:users /home/user
+
 {% if not webengine %}
 RUN pacman -U --noconfirm \
     https://archive.archlinux.org/packages/q/qt5-webkit/qt5-webkit-5.212.0alpha4-18-x86_64.pkg.tar.zst \
     https://archive.archlinux.org/packages/p/python-pyqt5/python-pyqt5-5.15.7-2-x86_64.pkg.tar.zst \
-    https://archive.archlinux.org/packages/p/python/python-3.10.10-1-x86_64.pkg.tar.zst \
     https://archive.archlinux.org/packages/i/icu/icu-72.1-2-x86_64.pkg.tar.zst \
     https://archive.archlinux.org/packages/l/libxml2/libxml2-2.10.4-4-x86_64.pkg.tar.zst \
     https://archive.archlinux.org/packages/q/qt5-base/qt5-base-5.15.10%2Bkde%2Br129-3-x86_64.pkg.tar.zst \
@@ -49,8 +52,15 @@ RUN pacman -U --noconfirm \
     https://archive.archlinux.org/packages/q/qt5-sensors/qt5-sensors-5.15.10-1-x86_64.pkg.tar.zst \
     https://archive.archlinux.org/packages/q/qt5-location/qt5-location-5.15.10%2Bkde%2Br5-1-x86_64.pkg.tar.zst \
     https://archive.archlinux.org/packages/q/qt5-webchannel/qt5-webchannel-5.15.10%2Bkde%2Br3-1-x86_64.pkg.tar.zst
+RUN pacman -S --noconfirm base-devel
 
-RUN python3 -m ensurepip
+RUN echo 'user ALL=(ALL) NOPASSWD:ALL' >> /etc/sudoers  # needed for makepkg
+USER user
+RUN cd ~ && \
+    git clone https://aur.archlinux.org/python310.git && \
+    cd python310 && \
+    makepkg -si --noconfirm
+USER root
 RUN python3 -m pip install tox pyqt5-sip
 {% endif %}
 
@@ -65,9 +75,6 @@ RUN python3 -m pip install tox pyqt5-sip
   RUN python3 -c "from {{ pyqt_module }} import QtWebKit, QtWebKitWidgets"
 {% endif %}
 
-RUN useradd user -u 1001 && \
-    mkdir /home/user && \
-    chown user:users /home/user
 USER user
 WORKDIR /home/user
 RUN git config --global --add safe.directory /outside/.git