test-pager: make the test compatible with chg
D911 tried to make this test compatible with chg but instead resulted
in the test being flaky for chg. For now, disabling this test for chg because
it seems difficult to fix the test. This will allow for the continuous build
setup for chg.
Test Plan:
Ran the test 'test-pager.t' with and without the '--chg' option.
Differential Revision: https://phab.mercurial-scm.org/D1128