Try with plain Ubuntu 18.04 instead of the Azure image

The Azure one fails with:

The following packages have unmet dependencies:
 libomp-dev : Depends: libomp5 (= 5.0.1-1)
E: Unable to correct problems, you have held broken packages.

Signed-off-by: Martin Tzvetanov Grigorov <mgrigorov@apache.org>

.github/workflows/ci.yaml

@@ -5,7 +5,9 @@ on: [push, pull_request]
 jobs:
   build:
     name: Build x86_64
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-latest
+    container:
+      image: ubuntu:18.04 # use plain Ubuntu 18.04 instead of the Azure one
     steps:
       - name: Checkout v3d_external
         uses: actions/checkout@v3
@@ -26,7 +28,7 @@ jobs:
         run: |
           set -x
           sudo apt-get update -q
-          sudo apt-get install -y clang-4.0 qt4-qmake libqt4-dev libqtcore4 libqtgui4 mesa-common-dev libglu1-mesa-dev libhdf5-dev libomp-dev
+          sudo apt-get install -y clang-4.0 git make qt4-qmake libqt4-dev libqtcore4 libqtgui4 mesa-common-dev libglu1-mesa-dev libhdf5-dev libtiff-dev libomp-dev
           sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/clang-4.0 40
           sudo update-alternatives --install /usr/bin/c++ c++ /usr/bin/clang++-4.0 40
           sudo update-alternatives --install /usr/bin/g++ g++ /usr/bin/clang++-4.0 40