Change back to 20.04

Author: hhoeflin

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

@@ -29,7 +29,7 @@ jobs:
           - {os: macOS-latest,   r: 'release'}
           - {os: macOS-latest,   r: 'devel'}
           - {os: macOS-latest,   r: '4.2.0', rspm: "https://packagemanager.rstudio.com/cran/latest"}
-          - {os: ubuntu-22.04,   r: 'release', rspm: "https://packagemanager.rstudio.com/cran/__linux__/bionic/latest"}
+          - {os: ubuntu-20.04,   r: 'release', rspm: "https://packagemanager.rstudio.com/cran/__linux__/bionic/latest"}
 
     env:
       R_REMOTES_NO_ERRORS_FROM_WARNINGS: true