Use same images for testing and artifact builds

Author: DimitrisStaratzis

.github/workflows/github_actions.yml

@@ -39,7 +39,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        os: [ ubuntu-18.04, macos-10.15 ]
+        os: [ ubuntu-latest, macos-10.15 ]
 
     steps:
        - name: checkout
@@ -86,7 +86,7 @@ jobs:
     if: startsWith(github.ref, 'refs/tags/')
     needs: [Test_Windows]
     name: Create_Artifacts_Windows
-    runs-on: windows-latest
+    runs-on: windows-2019
     steps:
       - name: checkout
         uses: actions/checkout@v2