Set newer Ubuntu version in workflow file

see actions/runner-images#11101

Author: hsonne

.github/workflows/R-CMD-check.yaml

@@ -23,7 +23,7 @@ jobs:
       matrix:
         config:
           - {os: macOS-latest, r: 'release'}
-          - {os: ubuntu-20.04, r: 'release', rspm: "https://packagemanager.rstudio.com/cran/__linux__/focal/latest"}
+          - {os: ubuntu-22.04, r: 'release', rspm: "https://packagemanager.rstudio.com/cran/__linux__/focal/latest"}
           - {os: windows-latest, r: 'devel'}
           - {os: windows-latest, r: 'oldrel'}
           - {os: windows-latest, r: 'release'}