Replace ubuntu-20.04 runner (#166)

Author: yvanlebras

.github/workflows/pr.yaml

@@ -190,7 +190,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        os: [ubuntu-20.04]
+        os: [ubuntu-24.04]
         r-version: ['release']
     steps:
     - name: lintr