CI: Run on ubuntu-latest

.github/workflows/build.yml

@@ -115,7 +115,7 @@ jobs:
           path: ./nightly/*.pkg
   ubuntu64:
     name: 'Linux/Ubuntu 64-bit'
-    runs-on: [ubuntu-18.04]
+    runs-on: [ubuntu-latest]
     steps:
       - name: Checkout
         uses: actions/checkout@v2.3.4
@@ -181,6 +181,8 @@ jobs:
            libqt5svg5-dev \
            swig \
            libxss-dev \
+           libx11-xcb-dev \
+           libxcb-xfixes0-dev \
            libopencv-dev
       - name: 'Configure'
         shell: bash