GHA: bump tested TF versions

Author: t-kalinowski

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

@@ -38,11 +38,12 @@ jobs:
           # - {os: 'windows-latest', tf: 'release', r: 'release'}
           # - {os: 'macOS-latest'  , tf: 'release', r: 'release'}
 
+          - {os: 'ubuntu-20.04', tf: '2.7', r: 'release'}
           - {os: 'ubuntu-20.04', tf: '2.6', r: 'release'}
           - {os: 'ubuntu-20.04', tf: '2.5', r: 'release'}
           - {os: 'ubuntu-20.04', tf: '2.4', r: 'release'}
           - {os: 'ubuntu-20.04', tf: '2.3', r: 'release'}
-          - {os: 'ubuntu-20.04', tf: '2.2', r: 'release'}
+          # - {os: 'ubuntu-20.04', tf: '2.2', r: 'release'}
 
           # these are allowed to fail
           # - {os: 'ubuntu-20.04', tf: 'default', r: 'devel'}