CI: Bump ubuntu version

20.04 runner being shut down soon

Author: cookpa

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

@@ -21,7 +21,7 @@ jobs:
         config:
           - {os: windows-latest, r: 'release'}
           - {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__/jammy/latest"}
 
     env:
       R_REMOTES_NO_ERRORS_FROM_WARNINGS: true