ADD GCC 7 and 8

Author: hartwork

.github/workflows/run_test_suite.yml

@@ -36,6 +36,10 @@ jobs:
       fail-fast: false
       matrix:
         include:
+          - runs-on: ubuntu-20.04
+            gcc: 7
+          - runs-on: ubuntu-20.04
+            gcc: 8
           - runs-on: ubuntu-22.04
             gcc: 9
           - runs-on: ubuntu-22.04