GitHub deprecated ubuntu-18.04 runners.

Author: rdzman

.github/workflows/continuous-integration.yml

@@ -13,8 +13,8 @@ jobs:
       fail-fast: false
       matrix:
         platform: [octave]
-#        os: [macos-10.15, macos-11.0, ubuntu-16.04, ubuntu-18.04, ubuntu-20.04]
-        os: [macos-latest, ubuntu-18.04, ubuntu-20.04]
+#        os: [macos-10.15, macos-11.0, macos-12.0, ubuntu-18.04, ubuntu-20.04, ubuntu-22.04]
+        os: [macos-latest, ubuntu-20.04, ubuntu-22.04]
         include:
         - platform: matlab
           os: ubuntu-latest