Re-instate checks against older versions

Author: HorridTom

.github/workflows/check-full.yaml

@@ -24,14 +24,14 @@ jobs:
 
           - {os: windows-latest, r: 'release'}
           # use 4.0 or 4.1 to check with rtools40's older compiler
-          #- {os: windows-latest, r: 'oldrel-4'}
+          - {os: windows-latest, r: 'oldrel-4'}
 
           - {os: ubuntu-latest,  r: 'devel', http-user-agent: 'release'}
           - {os: ubuntu-latest,  r: 'release'}
           - {os: ubuntu-latest,  r: 'oldrel-1'}
           - {os: ubuntu-latest,  r: 'oldrel-2'}
-          #- {os: ubuntu-latest,  r: 'oldrel-3'}
-          #- {os: ubuntu-latest,  r: 'oldrel-4'}
+          - {os: ubuntu-latest,  r: 'oldrel-3'}
+          - {os: ubuntu-latest,  r: 'oldrel-4'}
 
     env:
       GITHUB_PAT: ${{ secrets.GITHUB_TOKEN }}