GitHub Actions: add Linux Bionic / Qt 5.9 build

No artifacts from this build are preserved, this is just to make sure
that we can still build the desktop version against Qt 5.9.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>

.github/workflows/linux-bionic-5.9.yml

@@ -0,0 +1,29 @@
+name: Linux Qt 5.9
+on: push
+
+jobs:
+  buildOnBionic:
+    runs-on: ubuntu-18.04
+
+    steps:
+    - name: checkout sources
+      uses: actions/checkout@v1
+
+    - name: add build dependencies
+      run: |
+        sudo apt update
+        sudo apt install -y \
+        autoconf automake cmake g++ git libcrypto++-dev libcurl4-gnutls-dev \
+        libgit2-dev libqt5qml5 libqt5quick5 libqt5svg5-dev \
+        libqt5webkit5-dev libsqlite3-dev libssh2-1-dev libssl-dev libssl-dev \
+        libtool libusb-1.0-0-dev libxml2-dev libxslt1-dev libzip-dev make \
+        pkg-config qml-module-qtlocation qml-module-qtpositioning \
+        qml-module-qtquick2 qt5-default qt5-qmake qtchooser qtconnectivity5-dev \
+        qtdeclarative5-dev qtdeclarative5-private-dev qtlocation5-dev \
+        qtpositioning5-dev qtscript5-dev qttools5-dev qttools5-dev-tools \
+        qtquickcontrols2-5-dev
+
+    - name: run build
+      run: |
+        cd ..
+        bash -x subsurface/scripts/build.sh -desktop -build-with-webkit