patch 9.0.0264: CI still runs on Ubuntu 18.04

Problem:    CI still runs on Ubuntu 18.04.
Solution:   Run CI on Ubuntu 20.04. (closes #10582)

Author: pheiduck

.github/workflows/ci.yml

@@ -14,7 +14,7 @@ concurrency:
 
 jobs:
   linux:
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-20.04
 
     env:
       CC: ${{ matrix.compiler }}
@@ -167,11 +167,6 @@ jobs:
             # Use llvm-cov instead of gcov when compiler is clang.
             ln -fs /usr/bin/llvm-cov ${HOME}/bin/gcov
           fi
-          # Setup lua5.3 manually since its package doesn't provide alternative.
-          # https://bugs.launchpad.net/ubuntu/+source/lua5.3/+bug/1707212
-          if [[ ${CONFOPT} =~ luainterp ]]; then
-            sudo update-alternatives --install /usr/bin/lua lua /usr/bin/lua5.3 10
-          fi
           sudo sysctl -w net.ipv6.conf.lo.disable_ipv6=0
           sudo usermod -a -G audio "${USER}"
           sudo bash ci/setup-xvfb.sh
@@ -268,7 +263,7 @@ jobs:
           done
 
   # coveralls:
-  #   runs-on: ubuntu-18.04
+  #   runs-on: ubuntu-20.04
   #
   #   needs: linux
   #   if: always() && github.event_name != 'pull_request'

src/version.c

@@ -731,6 +731,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    264,
 /**/
     263,
 /**/