update the CI R versions

Author: MichaelChirico

.github/workflows/run_job.yaml

@@ -20,9 +20,9 @@ jobs:
       matrix:
         config:
           - {os: windows-latest, r: 'devel'}
-          - {os: windows-latest, r: '3.6'}
-          - {os: macOS-latest, r: '3.6'}
-          - {os: ubuntu-16.04, r: '3.6', cran: "https://demo.rstudiopm.com/all/__linux__/xenial/latest"}
+          - {os: windows-latest, r: '3.6.3'}
+          - {os: macOS-latest, r: '3.6.3'}
+          - {os: ubuntu-18.04, r: '4.0', cran: "https://demo.rstudiopm.com/all/__linux__/xenial/latest"}
 
     env:
       R_REMOTES_NO_ERRORS_FROM_WARNINGS: true