main: fix pager logic after negation cleanup

The pager setting is tristate (where None means "auto"),
so make sure we still handle that setting.

Change-Id: I89fe352572dd15922c61e3bb65ac33f847d01ee0
Test: `repo help upload` triggers the pager
Test: `repo -p help upload` triggers the pager
Test: `repo --no-pager help upload` doesn't trigger the pager
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/255852
Tested-by: Mike Frysinger <vapier@google.com>
Reviewed-by: David Pursehouse <dpursehouse@collab.net>

main.py

@@ -222,7 +222,7 @@ class _Repo(object):
             file=sys.stderr)
       return 1
 
-    if gopts.pager and not isinstance(cmd, InteractiveCommand):
+    if gopts.pager is not False and not isinstance(cmd, InteractiveCommand):
       config = cmd.manifest.globalConfig
       if gopts.pager:
         use_pager = True