Clean up stubsabot output

[srittau]

Currently, stubsabot's CI job (for example here) prints some extra information that we should hide by default:

• Branch switching:

  Switched to a new branch 'stubsabot/protobuf'
  branch 'stubsabot/protobuf' set up to track 'origin/main'.
  [stubsabot/protobuf d9d9cc807] [stubsabot] Bump protobuf to ~=7.35.1
   1 file changed, 1 insertion(+), 1 deletion(-)
  

  In these cases the usual protobuf... <action> output is missing and should be added.
• No push required:

  docutils... updating from '==0.22.3' to '==0.23'
  No pushing to origin required: origin/stubsabot/docutils exists and requires no changes!
  

  This happens when a previous stubsabot run already opened a PR, which is up-to-date. We should probably change the output to: "docutils... skipping (PR current)"
• dateparser errors:

  Switched to a new branch 'stubsabot/dateparser'
  branch 'stubsabot/dateparser' set up to track 'origin/main'.
  [stubsabot/dateparser f9ca8e0bd] [stubsabot] Bump dateparser to 1.4.2
   1 file changed, 1 insertion(+), 1 deletion(-)
  fatal: ambiguous argument 'stubsabot/dateparser...origin/stubsabot/dateparser': unknown revision or path not in the working tree.
  Use '--' to separate paths from revisions, like this:
  'git <command> [<revision>...] -- [<file>...]'
  remote: 
  remote: Create a pull request for 'stubsabot/dateparser' on GitHub by visiting:        
  remote:      https://github.com/python/typeshed/pull/new/stubsabot/dateparser        
  remote: 
  To github.com:python/typeshed.git
   * [new branch]          stubsabot/dateparser -> stubsabot/dateparser