test-help: don't use progress extension for the test of argument parsing

The next patch will remove the progress extension completely, so we have
to pick another extension. The schemes is picked arbitrary.

This test was introduced at 69da16b366ad.

tests/test-help.t

@@ -1028,12 +1028,12 b' Test help hooks'
 
 Test -e / -c / -k combinations
 
-  $ hg help -c progress
-  abort: no such help topic: progress
-  (try "hg help --keyword progress")
+  $ hg help -c schemes
+  abort: no such help topic: schemes
+  (try "hg help --keyword schemes")
   [255]
-  $ hg help -e progress |head -1
-  progress extension - show progress bars for some actions (DEPRECATED)
+  $ hg help -e schemes |head -1
+  schemes extension - extend schemes with shortcuts to repository swarms
   $ hg help -c -k dates |egrep '^(Topics|Extensions|Commands):'
   Commands:
   $ hg help -e -k a |egrep '^(Topics|Extensions|Commands):'