ci: Switch to GitHub actions

Travis has been long dead.

.github/workflows/test.yaml

@@ -0,0 +1,69 @@
+name: Test
+
+on:
+    - push
+    - pull_request
+
+jobs:
+    linux:
+        name: Linux
+        runs-on: ubuntu-22.04
+        steps:
+            - uses: actions/checkout@v4
+            - name: "Install dependencies"
+              run: |
+                sudo apt-get update
+                sudo apt-get install -y \
+                  g++ \
+                  gettext \
+                  intltool \
+                  gir1.2-gtk-3.0 \
+                  libgtk-3-dev \
+                  libjson-c-dev \
+                  liblcms2-dev \
+                  libpng-dev \
+                  python3-dev \
+                  python-gi-dev \
+                  python3-gi-cairo \
+                  python3-nose \
+                  python3-numpy \
+                  python3-setuptools \
+                  swig \
+                  git \
+                  xvfb
+            - name: "Install libmypaint"
+              run: |
+                git clone https://github.com/mypaint/libmypaint
+                pushd libmypaint
+                ./autogen.sh
+                ./configure --prefix=/usr
+                make
+                sudo make install
+                popd
+                sudo rm -fr libmypaint
+            - name: "Install mypaint-brushes"
+              run: |
+                git clone https://github.com/mypaint/mypaint-brushes
+                pushd mypaint-brushes
+                ./autogen.sh
+                ./configure --prefix=/usr
+                make
+                sudo make install
+                popd
+                sudo rm -fr mypaint-brushes
+            - name: "Build mypaint"
+              run: |
+                which python3
+                python3 -m this
+                python3 --version
+                python3 setup.py build_ext
+                python3 setup.py build
+            - name: "Run tests"
+              run: |
+                python3 setup.py nosetests --tests lib
+                python3 setup.py test
+                python3 setup.py clean --all
+                MYPAINT_DEBUG=1 xvfb-run -a python setup.py demo --args='--run-and-quit'
+                sudo python3 setup.py managed_install
+                sudo python3 setup.py managed_uninstall
+                bash appimage/trigger_build.sh