Change CI versions

.github/workflows/publish.yml

@@ -15,7 +15,7 @@ on:
 jobs:
   publish:
     if: contains('["raub"]', github.actor)
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-16.04
     steps:
       - uses: actions/checkout@v2
       - name: Install Node.js

.github/workflows/validate.yml

@@ -12,7 +12,7 @@ jobs:
   Validate:
     strategy:
         matrix:
-          os: [ubuntu-latest, windows-latest, macos-latest]
+          os: [ubuntu-16.04, windows-latest, macos-10.15]
 
     runs-on: ${{ matrix.os }}