t1092: use GIT_PROGRESS_DELAY for consistent results

The t1092-sparse-checkout-compatibility.sh tests compare the stdout and stderr for several Git commands across both full checkouts, sparse checkouts with a full index, and sparse checkouts with a sparse index. Since these are direct comparisons, sometimes a progress indicator can flush at unpredictable points, especially on slower machines. This causes the tests to be flaky. One standard way to avoid this is to add GIT_PROGRESS_DELAY=0 to the Git commands that are run, as this will force every progress indicator created with start_progress_delay() to be created immediately. However, there are some progress indicators that are created in the case of a full index that are not created with a sparse index. Moreover, their values may be different as those indexes have a different number of entries. Instead, use GIT_PROGRESS_DELAY=-1 (which will turn into UINT_MAX) to ensure that any reasonable machine running these tests would never display delayed progress indicators. Signed-off-by: Derrick Stolee <dstolee@microsoft.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>