t5400,t5402: consistently indent with tabs, not with spaces

t5400,t5402: consistently indent with tabs, not with spaces

This patch actually prepares for the upcoming patches to replace
`master` with `main` in these tests: we do not want those changes to be
flagged by the new `check-whitespace` GitHub workflow (even if those
changes do not introduce the whitespace issues, they touch lines
affected by those issues without fixing them).

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>