ci: Add a self-hosted runner

So we can use local machines to reduce ci times

.github/docker/Dockerfile

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+#
+# This file is part of KDDockWidgets.
+#
+# SPDX-FileCopyrightText: 2025 Klarälvdalens Datakonsult AB, a KDAB Group company <[email protected]>
+# Author: Sérgio Martins <[email protected]>
+#
+# SPDX-License-Identifier: GPL-2.0-only OR GPL-3.0-only
+#
+# Contact KDAB at <[email protected]> for commercial licensing options.
+
+# Docker container used by self-hosted runner
+
+# docker build --build-arg GITHUB_RUNNER_TOKEN=<TOKEN> -t kddw_gh_runner .
+# docker run -it kddw_gh_runner /home/ubuntu/actions-runner/run.sh
+
+FROM ubuntu:24.04
+MAINTAINER Sergio Martins ([email protected])
+
+ARG GITHUB_RUNNER_TOKEN
+
+ENV TZ=Europe/Berlin
+ENV LC_CTYPE=C.UTF-8
+ENV PATH=/home/ubuntu/.local/bin:$PATH
+
+RUN ln -snf /usr/share/zoneinfo/$TZ /etc/localtime && echo $TZ > /etc/timezone
+
+RUN apt update -qq && apt install build-essential software-properties-common lld git cmake ninja-build vim curl wget gdebi-core libdbus-glib-1-2 \
+        mesa-common-dev libglu1-mesa-dev libglib2.0-dev libfontconfig \
+        libxkbcommon-dev mesa-utils libgl1-mesa-dev libglu1-mesa-dev \
+        libxkbcommon-x11-0 libssl-dev openssl unzip clang libgtk-3-dev \
+        time xvfb python3-pip jq sudo -y
+
+RUN ln -s /usr/bin/python3 /usr/bin/python
+RUN rm /usr/lib/python3.12/EXTERNALLY-MANAGED
+
+# Install GitHub command-line interface (gh)
+# Instructions copied from https://github.com/cli/cli/blob/trunk/docs/install_linux.md
+RUN mkdir -p -m 755 /etc/apt/keyrings \
+    && curl -s https://cli.github.com/packages/githubcli-archive-keyring.gpg | tee /etc/apt/keyrings/githubcli-archive-keyring.gpg > /dev/null \
+    && chmod go+r /etc/apt/keyrings/githubcli-archive-keyring.gpg \
+    && echo "deb [arch=$(dpkg --print-architecture) signed-by=/etc/apt/keyrings/githubcli-archive-keyring.gpg] https://cli.github.com/packages stable main" | tee /etc/apt/sources.list.d/github-cli.list > /dev/null \
+    && apt-get update \
+    && apt-get install gh -y \
+    && apt-get clean \
+    && rm -rf /var/lib/apt/lists/*
+
+RUN usermod -aG sudo ubuntu
+RUN echo 'ubuntu ALL=(ALL) NOPASSWD:ALL' > /etc/sudoers.d/ubuntu
+RUN chmod 0440 /etc/sudoers.d/ubuntu
+
+USER ubuntu
+WORKDIR /home/ubuntu
+
+
+# Install GitHub Actions runner
+RUN mkdir actions-runner && cd actions-runner && \
+    curl -o actions-runner-linux-x64-2.321.0.tar.gz -L https://github.com/actions/runner/releases/download/v2.321.0/actions-runner-linux-x64-2.321.0.tar.gz && \
+    echo "ba46ba7ce3a4d7236b16fbe44419fb453bc08f866b24f04d549ec89f1722a29e  actions-runner-linux-x64-2.321.0.tar.gz" | shasum -a 256 -c && \
+    tar xzf ./actions-runner-linux-x64-2.321.0.tar.gz && ./config.sh --labels ubuntu-latest --url https://github.com/KDAB/KDDockWidgets --token $GITHUB_RUNNER_TOKEN

.github/docker/compose.yml

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+# SPDX-FileCopyrightText: 2024 Klarälvdalens Datakonsult AB, a KDAB Group company <[email protected]>
+#
+# SPDX-License-Identifier: GPL-2.0-only OR GPL-3.0-only
+
+services:
+  github-runner:
+    image: kddw_gh_runner
+    command: /home/ubuntu/actions-runner/run.sh
+    restart: always