Remove http-user-agent from Ubuntu job

Author: thackl

.github/workflows/main.yml

@@ -30,7 +30,7 @@ jobs:
           # use 4.0 or 4.1 to check with rtools40's older compiler
           # - {os: windows-latest, r: 'oldrel-4'}
 
-          - {os: ubuntu-latest,  r: 'devel', http-user-agent: 'release'}
+          - {os: ubuntu-latest,  r: 'devel'}
           # - {os: ubuntu-latest,  r: 'release'}
     env:
       GITHUB_PAT: ${{ secrets.GITHUB_TOKEN }}