Merge pull request #712 from ARTbio/upgrade_ubuntu_actions

drop ubuntu 20.04 for latest

Author: drosofff

.github/workflows/pr.yaml

@@ -185,7 +185,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        os: [ubuntu-20.04]
+        os: [ubuntu-latest]
         r-version: ['release']
     steps:
     - uses: actions/checkout@v4