Fix input completion tests on Qt6 & run tests on 22.04 (#4774)

* Tests: Fix InputCompletion tests in Qt6

This is achieved by not checking exact order for certain completion tests

* Tests: Use Ubuntu 22.04 for all tests

This allows us to be a bit more loose and use more C++20 features in
tests

* Update dockerfiles

.docker/Dockerfile-ubuntu-20.04-base

@@ -0,0 +1,38 @@
+FROM ubuntu:20.04
+
+ENV TZ=UTC
+RUN ln -snf /usr/share/zoneinfo/$TZ /etc/localtime && echo $TZ > /etc/timezone
+
+RUN apt-get update && apt-get -y install --no-install-recommends \
+        cmake \
+        virtualenv \
+        rapidjson-dev \
+        libfuse2 \
+        libssl-dev \
+        libboost-dev \
+        libxcb-randr0-dev \
+        libboost-system-dev \
+        libboost-filesystem-dev \
+        libpulse-dev \
+        libxkbcommon-x11-0 \
+        build-essential \
+        libgl1-mesa-dev \
+        libxcb-icccm4 \
+        libxcb-image0 \
+        libxcb-keysyms1 \
+        libxcb-render-util0 \
+        libxcb-xinerama0
+
+RUN apt-get -y install \
+        git \
+        lsb-release \
+        python3-pip && \
+        apt-get clean all
+
+# Install Qt as we do in CI
+
+RUN pip3 install -U pip && \
+        pip3 install aqtinstall && \
+        aqt install-qt linux desktop 5.12.12 && \
+        mkdir -p /opt/qt512 && \
+        mv /5.12.12/gcc_64/* /opt/qt512