Remove old Ubntu LTS

This version is becoming deprecated and is not widely used anymore

Author: feliwir

.github/workflows/linux.yml

@@ -23,7 +23,7 @@ jobs:
       fail-fast: false
       matrix:
         platform: [clang, gcc]
-        os: [ubuntu-18.04, ubuntu-20.04, ubuntu-22.04]
+        os: [ubuntu-20.04, ubuntu-22.04]
 
     steps:
       - uses: actions/checkout@v2