use ubuntu 18.04 -> 16.04

Author: GerryFerdinandus

.github/workflows/github_lazarus.yml

@@ -11,7 +11,7 @@ jobs:
     runs-on: ${{ matrix.operating-system }}
     strategy:
       matrix:
-        operating-system: [ubuntu-18.04,windows-latest]
+        operating-system: [ubuntu-16.04,windows-latest]
         lazarus-versions: [1.8.2]
     steps:
     - uses: actions/checkout@v2